| Message ID | 1615943798-14296-1-git-send-email-vincent.chen@sifive.com |
|---|---|
| Headers | show |
| Series | Support position independent execution | expand |
> -----Original Message----- > From: opensbi <opensbi-bounces@lists.infradead.org> On Behalf Of Vincent > Chen > Sent: 17 March 2021 06:47 > To: opensbi@lists.infradead.org > Cc: Vincent Chen <vincent.chen@sifive.com> > Subject: [PATCH v3 0/2] Support position independent execution > > This patch set enables OpenSBI to support position-independent execution > so that one OpenSBI generic firmware can run on multiple platforms, even if > they have different memory base addresses. However, the PIC code will > decrease a bit of performance. > > The performance loss of PIC comes from two additional operations. One is > from the symbol relocation in the beginning stage, and another one is from > the GOT reference (auipc + load GOT) in the OpenSBI lifetime. The former > only affects the boot time, but the latter will affect the performance of the > OpenSBI payload such as the Linux kernel. After analyzing the fw_payload.elf > of the generic platform, 27 symbols use the GOT reference method to get > their address. Fortunately, 17 of these symbols are accessed once during the > initialized step. Only the remaining > 10 symbols may be called repeatedly during the lifetime, which are 1. > hartid_to_domain_table 2. hartid_to_scratch_table 3. > sbi_hart_expected_trap 4. sbi_tlb_local_hfence_vvma 5. > sbi_tlb_local_hfence_gvma 6. sbi_tlb_local_sfence_vma_asid 7. > sbi_tlb_local_fence_i 8. sbi_tlb_local_hfence_gvma 9. > sbi_tlb_local_hfence_vvma 10. sbi_tlb_local_sfence_vma From these 10 > symbols, I think the IPI handler may be one of the critical and commonly used > paths affected by the PIC mode. Therefore, I create two kernel modules, > One keeps issuing the REMOTE_FENCE_I request and the other one keeps > issuing REMOTE_SFENCE_VMA request. These two modules are executed on > the unleashed board to measure the consumed time of the > sbi_tlb_request(). > I found the PIC causes a 1.6% and 4.1% performance loss in addressing > REMOTE_FENCE_I and REMOTE_SFENCE_VMA, respectively. In addition, to > observe the impact of PIC mode in the general usage cases, I use SPEC2006 > to benchmark performance. However, I could not observe any performance > impact from the results. Based on the above two results, I think the > performance impact of the PIC may not be obvious in general usage. Just in > case, this patch still creates an FW_PIC option for users to configure the build > options. > > Changes from v2 patch: > 1. Drop the relocation in FW_JUMP_FDT_ADDR, FW_JUMP_ADDR and > FW_PAYLOAD_FDT_ADDR. > 2. Code refinement > > Changes from v1 patch: > 1. Add -fpic to ASFLAGS and then remove the ".option pic" from fw_base.S 2. > Append the required flags to $(firmware-genflags-y), $(firmware-cflags-y) > and $(firmware-ldflags-y) instead of modifying top Makefile. > 3. Rearrange the patches > > Vincent Chen (2): > firmware: Use lla to access all global symbols > firmware: Support position independent execution This is a very good feature addition to OpenSBI. Thanks for doing it. Regards, Anup > > Makefile | 2 +- > firmware/fw_base.S | 150 +++++++++++++++++++++++++++++------- > ------ > firmware/fw_base.ldS | 13 ++++ > firmware/fw_dynamic.S | 18 ++--- > firmware/fw_jump.S | 2 +- > firmware/fw_payload.S | 2 +- > firmware/objects.mk | 7 ++ > firmware/payloads/test_head.S | 18 ++--- > include/sbi/riscv_elf.h | 14 ++++ > 9 files changed, 160 insertions(+), 66 deletions(-) create mode 100644 > include/sbi/riscv_elf.h > > -- > 2.7.4 > > > -- > opensbi mailing list > opensbi@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/opensbi