| Message ID | 20230921190429.1970766-1-i.maximets@ovn.org |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [ovs-dev,net-next] openvswitch: reduce stack usage in do_execute_actions | expand |
On Thu, Sep 21, 2023 at 9:03 PM Ilya Maximets <i.maximets@ovn.org> wrote: > > do_execute_actions() function can be called recursively multiple > times while executing actions that require pipeline forking or > recirculations. It may also be re-entered multiple times if the packet > leaves openvswitch module and re-enters it through a different port. > > Currently, there is a 256-byte array allocated on stack in this > function that is supposed to hold NSH header. Compilers tend to > pre-allocate that space right at the beginning of the function: > > a88: 48 81 ec b0 01 00 00 sub $0x1b0,%rsp > > NSH is not a very common protocol, but the space is allocated on every > recursive call or re-entry multiplying the wasted stack space. > > Move the stack allocation to push_nsh() function that is only used > if NSH actions are actually present. push_nsh() is also a simple > function without a possibility for re-entry, so the stack is returned > right away. > > With this change the preallocated space is reduced by 256 B per call: > > b18: 48 81 ec b0 00 00 00 sub $0xb0,%rsp > > Signed-off-by: Ilya Maximets <i.maximets@ovn.org> > --- > net/openvswitch/actions.c | 20 +++++++++----------- > 1 file changed, 9 insertions(+), 11 deletions(-) > > diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c > index 5f8094acd056..80cc5c512d7b 100644 > --- a/net/openvswitch/actions.c > +++ b/net/openvswitch/actions.c > @@ -312,10 +312,16 @@ static int push_eth(struct sk_buff *skb, struct sw_flow_key *key, > } > > static int push_nsh(struct sk_buff *skb, struct sw_flow_key *key, > - const struct nshhdr *nh) > + const struct nlattr *a) Presumably this function should be inlined. (one caller only) I would add noinline_for_stack to make sure the compiler will not play games with this attempt. > { > + u8 buffer[NSH_HDR_MAX_LEN]; > + struct nshhdr *nh = (struct nshhdr *)buffer; > int err; > > + err = nsh_hdr_from_nlattr(a, nh, NSH_HDR_MAX_LEN); > + if (err) > + return err; > + > err = nsh_push(skb, nh); > if (err) > return err; > @@ -1439,17 +1445,9 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb, > err = pop_eth(skb, key); > break; > > - case OVS_ACTION_ATTR_PUSH_NSH: { > - u8 buffer[NSH_HDR_MAX_LEN]; > - struct nshhdr *nh = (struct nshhdr *)buffer; > - > - err = nsh_hdr_from_nlattr(nla_data(a), nh, > - NSH_HDR_MAX_LEN); > - if (unlikely(err)) > - break; > - err = push_nsh(skb, key, nh); > + case OVS_ACTION_ATTR_PUSH_NSH: > + err = push_nsh(skb, key, nla_data(a)); > break; > - } > > case OVS_ACTION_ATTR_POP_NSH: > err = pop_nsh(skb, key); > -- > 2.41.0 >
On 9/21/23 21:08, Eric Dumazet wrote: > On Thu, Sep 21, 2023 at 9:03 PM Ilya Maximets <i.maximets@ovn.org> wrote: >> >> do_execute_actions() function can be called recursively multiple >> times while executing actions that require pipeline forking or >> recirculations. It may also be re-entered multiple times if the packet >> leaves openvswitch module and re-enters it through a different port. >> >> Currently, there is a 256-byte array allocated on stack in this >> function that is supposed to hold NSH header. Compilers tend to >> pre-allocate that space right at the beginning of the function: >> >> a88: 48 81 ec b0 01 00 00 sub $0x1b0,%rsp >> >> NSH is not a very common protocol, but the space is allocated on every >> recursive call or re-entry multiplying the wasted stack space. >> >> Move the stack allocation to push_nsh() function that is only used >> if NSH actions are actually present. push_nsh() is also a simple >> function without a possibility for re-entry, so the stack is returned >> right away. >> >> With this change the preallocated space is reduced by 256 B per call: >> >> b18: 48 81 ec b0 00 00 00 sub $0xb0,%rsp >> >> Signed-off-by: Ilya Maximets <i.maximets@ovn.org> >> --- >> net/openvswitch/actions.c | 20 +++++++++----------- >> 1 file changed, 9 insertions(+), 11 deletions(-) >> >> diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c >> index 5f8094acd056..80cc5c512d7b 100644 >> --- a/net/openvswitch/actions.c >> +++ b/net/openvswitch/actions.c >> @@ -312,10 +312,16 @@ static int push_eth(struct sk_buff *skb, struct sw_flow_key *key, >> } >> >> static int push_nsh(struct sk_buff *skb, struct sw_flow_key *key, >> - const struct nshhdr *nh) >> + const struct nlattr *a) > > Presumably this function should be inlined. (one caller only) > > I would add noinline_for_stack to make sure the compiler will not play > games with this attempt. Yeah, good point! I didn't see it being inlined in my testing, but it's better to be sure. I'll post v2 with a flag. > >> { >> + u8 buffer[NSH_HDR_MAX_LEN]; >> + struct nshhdr *nh = (struct nshhdr *)buffer; >> int err; >> >> + err = nsh_hdr_from_nlattr(a, nh, NSH_HDR_MAX_LEN); >> + if (err) >> + return err; >> + >> err = nsh_push(skb, nh); >> if (err) >> return err; >> @@ -1439,17 +1445,9 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb, >> err = pop_eth(skb, key); >> break; >> >> - case OVS_ACTION_ATTR_PUSH_NSH: { >> - u8 buffer[NSH_HDR_MAX_LEN]; >> - struct nshhdr *nh = (struct nshhdr *)buffer; >> - >> - err = nsh_hdr_from_nlattr(nla_data(a), nh, >> - NSH_HDR_MAX_LEN); >> - if (unlikely(err)) >> - break; >> - err = push_nsh(skb, key, nh); >> + case OVS_ACTION_ATTR_PUSH_NSH: >> + err = push_nsh(skb, key, nla_data(a)); >> break; >> - } >> >> case OVS_ACTION_ATTR_POP_NSH: >> err = pop_nsh(skb, key); >> -- >> 2.41.0 >>
diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c index 5f8094acd056..80cc5c512d7b 100644 --- a/net/openvswitch/actions.c +++ b/net/openvswitch/actions.c @@ -312,10 +312,16 @@ static int push_eth(struct sk_buff *skb, struct sw_flow_key *key, } static int push_nsh(struct sk_buff *skb, struct sw_flow_key *key, - const struct nshhdr *nh) + const struct nlattr *a) { + u8 buffer[NSH_HDR_MAX_LEN]; + struct nshhdr *nh = (struct nshhdr *)buffer; int err; + err = nsh_hdr_from_nlattr(a, nh, NSH_HDR_MAX_LEN); + if (err) + return err; + err = nsh_push(skb, nh); if (err) return err; @@ -1439,17 +1445,9 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb, err = pop_eth(skb, key); break; - case OVS_ACTION_ATTR_PUSH_NSH: { - u8 buffer[NSH_HDR_MAX_LEN]; - struct nshhdr *nh = (struct nshhdr *)buffer; - - err = nsh_hdr_from_nlattr(nla_data(a), nh, - NSH_HDR_MAX_LEN); - if (unlikely(err)) - break; - err = push_nsh(skb, key, nh); + case OVS_ACTION_ATTR_PUSH_NSH: + err = push_nsh(skb, key, nla_data(a)); break; - } case OVS_ACTION_ATTR_POP_NSH: err = pop_nsh(skb, key);
do_execute_actions() function can be called recursively multiple times while executing actions that require pipeline forking or recirculations. It may also be re-entered multiple times if the packet leaves openvswitch module and re-enters it through a different port. Currently, there is a 256-byte array allocated on stack in this function that is supposed to hold NSH header. Compilers tend to pre-allocate that space right at the beginning of the function: a88: 48 81 ec b0 01 00 00 sub $0x1b0,%rsp NSH is not a very common protocol, but the space is allocated on every recursive call or re-entry multiplying the wasted stack space. Move the stack allocation to push_nsh() function that is only used if NSH actions are actually present. push_nsh() is also a simple function without a possibility for re-entry, so the stack is returned right away. With this change the preallocated space is reduced by 256 B per call: b18: 48 81 ec b0 00 00 00 sub $0xb0,%rsp Signed-off-by: Ilya Maximets <i.maximets@ovn.org> --- net/openvswitch/actions.c | 20 +++++++++----------- 1 file changed, 9 insertions(+), 11 deletions(-)