| Message ID | 20230607194643.2081329-2-goldstein.w.n@gmail.com |
|---|---|
| State | New |
| Headers | show |
| Series | [v1,1/2] linux: Implement sched_yield in C | expand |
On Wed, Jun 7, 2023 at 12:46 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote: > > xsave/xrstor have optimization to skip saving/restoring register > classes if those register classes are in the init state > (inuse[bit]==0). > > We can get: > SSE state > AVX state > ZMM_HI256 state > > to init state using `vzeroall`. Doing this before syscalls that will > cause a proper context switch can be beneficial in terms of the amount > of state the kernel needs to save/restore. This can save time and > memory. > --- > sysdeps/generic/prepare-context-switch.h | 28 +++++++++++++ > sysdeps/unix/sysv/linux/clock_nanosleep.c | 2 + > sysdeps/unix/sysv/linux/sched_yield.c | 2 + > sysdeps/x86/prepare-context-switch.h | 50 +++++++++++++++++++++++ > 4 files changed, 82 insertions(+) > create mode 100644 sysdeps/generic/prepare-context-switch.h > create mode 100644 sysdeps/x86/prepare-context-switch.h > > diff --git a/sysdeps/generic/prepare-context-switch.h b/sysdeps/generic/prepare-context-switch.h > new file mode 100644 > index 0000000000..6153847905 > --- /dev/null > +++ b/sysdeps/generic/prepare-context-switch.h > @@ -0,0 +1,28 @@ > +/* Prepare process for context switch. generic version > + Copyright (C) 2023 Free Software Foundation, Inc. > + This file is part of the GNU C Library. > + > + The GNU C Library is free software; you can redistribute it and/or > + modify it under the terms of the GNU Lesser General Public > + License as published by the Free Software Foundation; either > + version 2.1 of the License, or (at your option) any later version. > + > + The GNU C Library is distributed in the hope that it will be useful, > + but WITHOUT ANY WARRANTY; without even the implied warranty of > + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU > + Lesser General Public License for more details. > + > + You should have received a copy of the GNU Lesser General Public > + License along with the GNU C Library; if not, see > + <https://www.gnu.org/licenses/>. */ > + > +#ifndef _PREPARE_CONTEXT_SWITCH_H > +#define _PREPARE_CONTEXT_SWITCH_H > + > +static void > +prepare_context_switch (void) > +{ > + /* Empty. */ > +} > + > +#endif > diff --git a/sysdeps/unix/sysv/linux/clock_nanosleep.c b/sysdeps/unix/sysv/linux/clock_nanosleep.c > index ac2d810632..e674f0ac54 100644 > --- a/sysdeps/unix/sysv/linux/clock_nanosleep.c > +++ b/sysdeps/unix/sysv/linux/clock_nanosleep.c > @@ -23,6 +23,7 @@ > #include "kernel-posix-cpu-timers.h" > > #include <shlib-compat.h> > +#include <prepare-context-switch.h> > > /* We can simply use the syscall. The CPU clocks are not supported > with this function. */ > @@ -44,6 +45,7 @@ __clock_nanosleep_time64 (clockid_t clock_id, int flags, > #endif > > int r; > + prepare_context_switch(); > #ifdef __ASSUME_TIME64_SYSCALLS > r = INTERNAL_SYSCALL_CANCEL (clock_nanosleep_time64, clock_id, flags, req, > rem); > diff --git a/sysdeps/unix/sysv/linux/sched_yield.c b/sysdeps/unix/sysv/linux/sched_yield.c > index 154bf725b0..d26c0f8a9f 100644 > --- a/sysdeps/unix/sysv/linux/sched_yield.c > +++ b/sysdeps/unix/sysv/linux/sched_yield.c > @@ -17,10 +17,12 @@ > <https://www.gnu.org/licenses/>. */ > > #include <sysdep.h> > +#include <prepare-context-switch.h> > > int > __sched_yield (void) > { > + prepare_context_switch(); > return INLINE_SYSCALL_CALL (sched_yield); > } > libc_hidden_def (__sched_yield); > diff --git a/sysdeps/x86/prepare-context-switch.h b/sysdeps/x86/prepare-context-switch.h > new file mode 100644 > index 0000000000..bf33a7a1b3 > --- /dev/null > +++ b/sysdeps/x86/prepare-context-switch.h > @@ -0,0 +1,50 @@ > +/* Prepare process for context switch. x86 version > + Copyright (C) 2023 Free Software Foundation, Inc. > + This file is part of the GNU C Library. > + > + The GNU C Library is free software; you can redistribute it and/or > + modify it under the terms of the GNU Lesser General Public > + License as published by the Free Software Foundation; either > + version 2.1 of the License, or (at your option) any later version. > + > + The GNU C Library is distributed in the hope that it will be useful, > + but WITHOUT ANY WARRANTY; without even the implied warranty of > + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU > + Lesser General Public License for more details. > + > + You should have received a copy of the GNU Lesser General Public > + License along with the GNU C Library; if not, see > + <https://www.gnu.org/licenses/>. */ > + > +#ifndef _PREPARE_CONTEXT_SWITCH_H > +#define _PREPARE_CONTEXT_SWITCH_H > + > +#ifdef __AVX__ Please use if (CPU_FEATURE_ACTIVE (AVX)) to detect it at run-time. > +static void > +prepare_context_switch (void) > +{ > + /* vzeroall before context switch will restore xsave/xrstor state of the > + following to init state: > + - SSE state > + - AVX state > + - ZMM_HI256 state > + This saves a touch of overhead and memory in context switches. > + This function can/should be used before an operation that will > + cause a context switch in the current process (sched_yield, > + *sleep, etc...). > + */ > + __asm__ volatile ("vzeroall" Can you use _mm256_zeroall? > + : > + : > + : "zmm0", "zmm1", "zmm2", "zmm3", "zmm4", "zmm5", "zmm6", > + "zmm7", "zmm8", "zmm9", "zmm10", "zmm11", "zmm12", > + "zmm13", "zmm14", "zmm15"); > + /* TODO: Add xtilerelease for amx state. */ > +} > + > +#else > +# undef _PREPARE_CONTEXT_SWITCH_H > +# include <sysdeps/generic/prepare-context-switch.h> > +#endif > + > +#endif > -- > 2.34.1 >
On Wed, Jun 7, 2023 at 3:46 PM H.J. Lu <hjl.tools@gmail.com> wrote: > > On Wed, Jun 7, 2023 at 12:46 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote: > > > > xsave/xrstor have optimization to skip saving/restoring register > > classes if those register classes are in the init state > > (inuse[bit]==0). > > > > We can get: > > SSE state > > AVX state > > ZMM_HI256 state > > > > to init state using `vzeroall`. Doing this before syscalls that will > > cause a proper context switch can be beneficial in terms of the amount > > of state the kernel needs to save/restore. This can save time and > > memory. > > --- > > sysdeps/generic/prepare-context-switch.h | 28 +++++++++++++ > > sysdeps/unix/sysv/linux/clock_nanosleep.c | 2 + > > sysdeps/unix/sysv/linux/sched_yield.c | 2 + > > sysdeps/x86/prepare-context-switch.h | 50 +++++++++++++++++++++++ > > 4 files changed, 82 insertions(+) > > create mode 100644 sysdeps/generic/prepare-context-switch.h > > create mode 100644 sysdeps/x86/prepare-context-switch.h > > > > diff --git a/sysdeps/generic/prepare-context-switch.h b/sysdeps/generic/prepare-context-switch.h > > new file mode 100644 > > index 0000000000..6153847905 > > --- /dev/null > > +++ b/sysdeps/generic/prepare-context-switch.h > > @@ -0,0 +1,28 @@ > > +/* Prepare process for context switch. generic version > > + Copyright (C) 2023 Free Software Foundation, Inc. > > + This file is part of the GNU C Library. > > + > > + The GNU C Library is free software; you can redistribute it and/or > > + modify it under the terms of the GNU Lesser General Public > > + License as published by the Free Software Foundation; either > > + version 2.1 of the License, or (at your option) any later version. > > + > > + The GNU C Library is distributed in the hope that it will be useful, > > + but WITHOUT ANY WARRANTY; without even the implied warranty of > > + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU > > + Lesser General Public License for more details. > > + > > + You should have received a copy of the GNU Lesser General Public > > + License along with the GNU C Library; if not, see > > + <https://www.gnu.org/licenses/>. */ > > + > > +#ifndef _PREPARE_CONTEXT_SWITCH_H > > +#define _PREPARE_CONTEXT_SWITCH_H > > + > > +static void > > +prepare_context_switch (void) > > +{ > > + /* Empty. */ > > +} > > + > > +#endif > > diff --git a/sysdeps/unix/sysv/linux/clock_nanosleep.c b/sysdeps/unix/sysv/linux/clock_nanosleep.c > > index ac2d810632..e674f0ac54 100644 > > --- a/sysdeps/unix/sysv/linux/clock_nanosleep.c > > +++ b/sysdeps/unix/sysv/linux/clock_nanosleep.c > > @@ -23,6 +23,7 @@ > > #include "kernel-posix-cpu-timers.h" > > > > #include <shlib-compat.h> > > +#include <prepare-context-switch.h> > > > > /* We can simply use the syscall. The CPU clocks are not supported > > with this function. */ > > @@ -44,6 +45,7 @@ __clock_nanosleep_time64 (clockid_t clock_id, int flags, > > #endif > > > > int r; > > + prepare_context_switch(); > > #ifdef __ASSUME_TIME64_SYSCALLS > > r = INTERNAL_SYSCALL_CANCEL (clock_nanosleep_time64, clock_id, flags, req, > > rem); > > diff --git a/sysdeps/unix/sysv/linux/sched_yield.c b/sysdeps/unix/sysv/linux/sched_yield.c > > index 154bf725b0..d26c0f8a9f 100644 > > --- a/sysdeps/unix/sysv/linux/sched_yield.c > > +++ b/sysdeps/unix/sysv/linux/sched_yield.c > > @@ -17,10 +17,12 @@ > > <https://www.gnu.org/licenses/>. */ > > > > #include <sysdep.h> > > +#include <prepare-context-switch.h> > > > > int > > __sched_yield (void) > > { > > + prepare_context_switch(); > > return INLINE_SYSCALL_CALL (sched_yield); > > } > > libc_hidden_def (__sched_yield); > > diff --git a/sysdeps/x86/prepare-context-switch.h b/sysdeps/x86/prepare-context-switch.h > > new file mode 100644 > > index 0000000000..bf33a7a1b3 > > --- /dev/null > > +++ b/sysdeps/x86/prepare-context-switch.h > > @@ -0,0 +1,50 @@ > > +/* Prepare process for context switch. x86 version > > + Copyright (C) 2023 Free Software Foundation, Inc. > > + This file is part of the GNU C Library. > > + > > + The GNU C Library is free software; you can redistribute it and/or > > + modify it under the terms of the GNU Lesser General Public > > + License as published by the Free Software Foundation; either > > + version 2.1 of the License, or (at your option) any later version. > > + > > + The GNU C Library is distributed in the hope that it will be useful, > > + but WITHOUT ANY WARRANTY; without even the implied warranty of > > + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU > > + Lesser General Public License for more details. > > + > > + You should have received a copy of the GNU Lesser General Public > > + License along with the GNU C Library; if not, see > > + <https://www.gnu.org/licenses/>. */ > > + > > +#ifndef _PREPARE_CONTEXT_SWITCH_H > > +#define _PREPARE_CONTEXT_SWITCH_H > > + > > +#ifdef __AVX__ > > Please use > > if (CPU_FEATURE_ACTIVE (AVX)) > > to detect it at run-time. > Wanted to avoid overhead. Think if we want runtime check should ifunc the functions we want to put it in (just clock_nanosleep64 and sched_yield). WDYT? > > +static void > > +prepare_context_switch (void) > > +{ > > + /* vzeroall before context switch will restore xsave/xrstor state of the > > + following to init state: > > + - SSE state > > + - AVX state > > + - ZMM_HI256 state > > + This saves a touch of overhead and memory in context switches. > > + This function can/should be used before an operation that will > > + cause a context switch in the current process (sched_yield, > > + *sleep, etc...). > > + */ > > + __asm__ volatile ("vzeroall" > > Can you use _mm256_zeroall? > > > + : > > + : > > + : "zmm0", "zmm1", "zmm2", "zmm3", "zmm4", "zmm5", "zmm6", > > + "zmm7", "zmm8", "zmm9", "zmm10", "zmm11", "zmm12", > > + "zmm13", "zmm14", "zmm15"); > > + /* TODO: Add xtilerelease for amx state. */ > > +} > > + > > +#else > > +# undef _PREPARE_CONTEXT_SWITCH_H > > +# include <sysdeps/generic/prepare-context-switch.h> > > +#endif > > + > > +#endif > > -- > > 2.34.1 > > > > > -- > H.J.
On Wed, Jun 7, 2023 at 4:59 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote: > > On Wed, Jun 7, 2023 at 3:46 PM H.J. Lu <hjl.tools@gmail.com> wrote: > > > > On Wed, Jun 7, 2023 at 12:46 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote: > > > > > > xsave/xrstor have optimization to skip saving/restoring register > > > classes if those register classes are in the init state > > > (inuse[bit]==0). > > > > > > We can get: > > > SSE state > > > AVX state > > > ZMM_HI256 state > > > > > > to init state using `vzeroall`. Doing this before syscalls that will > > > cause a proper context switch can be beneficial in terms of the amount > > > of state the kernel needs to save/restore. This can save time and > > > memory. > > > --- > > > sysdeps/generic/prepare-context-switch.h | 28 +++++++++++++ > > > sysdeps/unix/sysv/linux/clock_nanosleep.c | 2 + > > > sysdeps/unix/sysv/linux/sched_yield.c | 2 + > > > sysdeps/x86/prepare-context-switch.h | 50 +++++++++++++++++++++++ > > > 4 files changed, 82 insertions(+) > > > create mode 100644 sysdeps/generic/prepare-context-switch.h > > > create mode 100644 sysdeps/x86/prepare-context-switch.h > > > > > > diff --git a/sysdeps/generic/prepare-context-switch.h b/sysdeps/generic/prepare-context-switch.h > > > new file mode 100644 > > > index 0000000000..6153847905 > > > --- /dev/null > > > +++ b/sysdeps/generic/prepare-context-switch.h > > > @@ -0,0 +1,28 @@ > > > +/* Prepare process for context switch. generic version > > > + Copyright (C) 2023 Free Software Foundation, Inc. > > > + This file is part of the GNU C Library. > > > + > > > + The GNU C Library is free software; you can redistribute it and/or > > > + modify it under the terms of the GNU Lesser General Public > > > + License as published by the Free Software Foundation; either > > > + version 2.1 of the License, or (at your option) any later version. > > > + > > > + The GNU C Library is distributed in the hope that it will be useful, > > > + but WITHOUT ANY WARRANTY; without even the implied warranty of > > > + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU > > > + Lesser General Public License for more details. > > > + > > > + You should have received a copy of the GNU Lesser General Public > > > + License along with the GNU C Library; if not, see > > > + <https://www.gnu.org/licenses/>. */ > > > + > > > +#ifndef _PREPARE_CONTEXT_SWITCH_H > > > +#define _PREPARE_CONTEXT_SWITCH_H > > > + > > > +static void > > > +prepare_context_switch (void) > > > +{ > > > + /* Empty. */ > > > +} > > > + > > > +#endif > > > diff --git a/sysdeps/unix/sysv/linux/clock_nanosleep.c b/sysdeps/unix/sysv/linux/clock_nanosleep.c > > > index ac2d810632..e674f0ac54 100644 > > > --- a/sysdeps/unix/sysv/linux/clock_nanosleep.c > > > +++ b/sysdeps/unix/sysv/linux/clock_nanosleep.c > > > @@ -23,6 +23,7 @@ > > > #include "kernel-posix-cpu-timers.h" > > > > > > #include <shlib-compat.h> > > > +#include <prepare-context-switch.h> > > > > > > /* We can simply use the syscall. The CPU clocks are not supported > > > with this function. */ > > > @@ -44,6 +45,7 @@ __clock_nanosleep_time64 (clockid_t clock_id, int flags, > > > #endif > > > > > > int r; > > > + prepare_context_switch(); > > > #ifdef __ASSUME_TIME64_SYSCALLS > > > r = INTERNAL_SYSCALL_CANCEL (clock_nanosleep_time64, clock_id, flags, req, > > > rem); > > > diff --git a/sysdeps/unix/sysv/linux/sched_yield.c b/sysdeps/unix/sysv/linux/sched_yield.c > > > index 154bf725b0..d26c0f8a9f 100644 > > > --- a/sysdeps/unix/sysv/linux/sched_yield.c > > > +++ b/sysdeps/unix/sysv/linux/sched_yield.c > > > @@ -17,10 +17,12 @@ > > > <https://www.gnu.org/licenses/>. */ > > > > > > #include <sysdep.h> > > > +#include <prepare-context-switch.h> > > > > > > int > > > __sched_yield (void) > > > { > > > + prepare_context_switch(); > > > return INLINE_SYSCALL_CALL (sched_yield); > > > } > > > libc_hidden_def (__sched_yield); > > > diff --git a/sysdeps/x86/prepare-context-switch.h b/sysdeps/x86/prepare-context-switch.h > > > new file mode 100644 > > > index 0000000000..bf33a7a1b3 > > > --- /dev/null > > > +++ b/sysdeps/x86/prepare-context-switch.h > > > @@ -0,0 +1,50 @@ > > > +/* Prepare process for context switch. x86 version > > > + Copyright (C) 2023 Free Software Foundation, Inc. > > > + This file is part of the GNU C Library. > > > + > > > + The GNU C Library is free software; you can redistribute it and/or > > > + modify it under the terms of the GNU Lesser General Public > > > + License as published by the Free Software Foundation; either > > > + version 2.1 of the License, or (at your option) any later version. > > > + > > > + The GNU C Library is distributed in the hope that it will be useful, > > > + but WITHOUT ANY WARRANTY; without even the implied warranty of > > > + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU > > > + Lesser General Public License for more details. > > > + > > > + You should have received a copy of the GNU Lesser General Public > > > + License along with the GNU C Library; if not, see > > > + <https://www.gnu.org/licenses/>. */ > > > + > > > +#ifndef _PREPARE_CONTEXT_SWITCH_H > > > +#define _PREPARE_CONTEXT_SWITCH_H > > > + > > > +#ifdef __AVX__ > > > > Please use > > > > if (CPU_FEATURE_ACTIVE (AVX)) > > > > to detect it at run-time. > > > Wanted to avoid overhead. Think if we want runtime check should ifunc > the functions > we want to put it in (just clock_nanosleep64 and sched_yield). WDYT? > > > > +static void > > > +prepare_context_switch (void) > > > +{ > > > + /* vzeroall before context switch will restore xsave/xrstor state of the > > > + following to init state: > > > + - SSE state > > > + - AVX state > > > + - ZMM_HI256 state > > > + This saves a touch of overhead and memory in context switches. > > > + This function can/should be used before an operation that will > > > + cause a context switch in the current process (sched_yield, > > > + *sleep, etc...). > > > + */ > > > + __asm__ volatile ("vzeroall" > > > > Can you use _mm256_zeroall? > > > > > + : > > > + : > > > + : "zmm0", "zmm1", "zmm2", "zmm3", "zmm4", "zmm5", "zmm6", > > > + "zmm7", "zmm8", "zmm9", "zmm10", "zmm11", "zmm12", > > > + "zmm13", "zmm14", "zmm15"); > > > + /* TODO: Add xtilerelease for amx state. */ > > > +} > > > + > > > +#else > > > +# undef _PREPARE_CONTEXT_SWITCH_H > > > +# include <sysdeps/generic/prepare-context-switch.h> > > > +#endif > > > + > > > +#endif > > > -- > > > 2.34.1 > > > > > > > > > -- > > H.J. Abandoning this patch in favor of the versions at: "x86: Implement sched_yield syscall for x86 only." and "x86: Implement clock_nanosleep{_time64} syscall for x86 only."
diff --git a/sysdeps/generic/prepare-context-switch.h b/sysdeps/generic/prepare-context-switch.h new file mode 100644 index 0000000000..6153847905 --- /dev/null +++ b/sysdeps/generic/prepare-context-switch.h @@ -0,0 +1,28 @@ +/* Prepare process for context switch. generic version + Copyright (C) 2023 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + <https://www.gnu.org/licenses/>. */ + +#ifndef _PREPARE_CONTEXT_SWITCH_H +#define _PREPARE_CONTEXT_SWITCH_H + +static void +prepare_context_switch (void) +{ + /* Empty. */ +} + +#endif diff --git a/sysdeps/unix/sysv/linux/clock_nanosleep.c b/sysdeps/unix/sysv/linux/clock_nanosleep.c index ac2d810632..e674f0ac54 100644 --- a/sysdeps/unix/sysv/linux/clock_nanosleep.c +++ b/sysdeps/unix/sysv/linux/clock_nanosleep.c @@ -23,6 +23,7 @@ #include "kernel-posix-cpu-timers.h" #include <shlib-compat.h> +#include <prepare-context-switch.h> /* We can simply use the syscall. The CPU clocks are not supported with this function. */ @@ -44,6 +45,7 @@ __clock_nanosleep_time64 (clockid_t clock_id, int flags, #endif int r; + prepare_context_switch(); #ifdef __ASSUME_TIME64_SYSCALLS r = INTERNAL_SYSCALL_CANCEL (clock_nanosleep_time64, clock_id, flags, req, rem); diff --git a/sysdeps/unix/sysv/linux/sched_yield.c b/sysdeps/unix/sysv/linux/sched_yield.c index 154bf725b0..d26c0f8a9f 100644 --- a/sysdeps/unix/sysv/linux/sched_yield.c +++ b/sysdeps/unix/sysv/linux/sched_yield.c @@ -17,10 +17,12 @@ <https://www.gnu.org/licenses/>. */ #include <sysdep.h> +#include <prepare-context-switch.h> int __sched_yield (void) { + prepare_context_switch(); return INLINE_SYSCALL_CALL (sched_yield); } libc_hidden_def (__sched_yield); diff --git a/sysdeps/x86/prepare-context-switch.h b/sysdeps/x86/prepare-context-switch.h new file mode 100644 index 0000000000..bf33a7a1b3 --- /dev/null +++ b/sysdeps/x86/prepare-context-switch.h @@ -0,0 +1,50 @@ +/* Prepare process for context switch. x86 version + Copyright (C) 2023 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + <https://www.gnu.org/licenses/>. */ + +#ifndef _PREPARE_CONTEXT_SWITCH_H +#define _PREPARE_CONTEXT_SWITCH_H + +#ifdef __AVX__ +static void +prepare_context_switch (void) +{ + /* vzeroall before context switch will restore xsave/xrstor state of the + following to init state: + - SSE state + - AVX state + - ZMM_HI256 state + This saves a touch of overhead and memory in context switches. + This function can/should be used before an operation that will + cause a context switch in the current process (sched_yield, + *sleep, etc...). + */ + __asm__ volatile ("vzeroall" + : + : + : "zmm0", "zmm1", "zmm2", "zmm3", "zmm4", "zmm5", "zmm6", + "zmm7", "zmm8", "zmm9", "zmm10", "zmm11", "zmm12", + "zmm13", "zmm14", "zmm15"); + /* TODO: Add xtilerelease for amx state. */ +} + +#else +# undef _PREPARE_CONTEXT_SWITCH_H +# include <sysdeps/generic/prepare-context-switch.h> +#endif + +#endif
xsave/xrstor have optimization to skip saving/restoring register classes if those register classes are in the init state (inuse[bit]==0). We can get: SSE state AVX state ZMM_HI256 state to init state using `vzeroall`. Doing this before syscalls that will cause a proper context switch can be beneficial in terms of the amount of state the kernel needs to save/restore. This can save time and memory. --- sysdeps/generic/prepare-context-switch.h | 28 +++++++++++++ sysdeps/unix/sysv/linux/clock_nanosleep.c | 2 + sysdeps/unix/sysv/linux/sched_yield.c | 2 + sysdeps/x86/prepare-context-switch.h | 50 +++++++++++++++++++++++ 4 files changed, 82 insertions(+) create mode 100644 sysdeps/generic/prepare-context-switch.h create mode 100644 sysdeps/x86/prepare-context-switch.h