| Message ID | 20230921194314.1976605-1-i.maximets@ovn.org (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 06bc3668cc2a6db2831b9086f0e3c6ebda599dba |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net-next,v2] openvswitch: reduce stack usage in do_execute_actions | expand |
On Thu, Sep 21, 2023 at 9:42 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. > Reviewed-by: Eric Dumazet <edumazet@google.com>
On 21 Sep 2023, at 21:42, Ilya Maximets 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> One more time to the list only, as for some reason I had HTML reply turned on :( Thanks Ilya for optimizing this. Reviewed-by: Eelco Chaudron echaudro@redhat.com
Ilya Maximets <i.maximets@ovn.org> writes: > 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> > --- Thanks, Ilya. Reviewed-by: Aaron Conole <aconole@redhat.com>
Hello: This patch was applied to netdev/net-next.git (main) by David S. Miller <davem@davemloft.net>: On Thu, 21 Sep 2023 21:42:35 +0200 you 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: > > [...] Here is the summary with links: - [net-next,v2] openvswitch: reduce stack usage in do_execute_actions https://git.kernel.org/netdev/net-next/c/06bc3668cc2a You are awesome, thank you!
diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c index 5f8094acd056..6fcd7e2ca81f 100644 --- a/net/openvswitch/actions.c +++ b/net/openvswitch/actions.c @@ -311,11 +311,18 @@ static int push_eth(struct sk_buff *skb, struct sw_flow_key *key, return 0; } -static int push_nsh(struct sk_buff *skb, struct sw_flow_key *key, - const struct nshhdr *nh) +static noinline_for_stack int push_nsh(struct sk_buff *skb, + struct sw_flow_key *key, + 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 +1446,9 @@ 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> --- Version 2: - Added 'noinline_for_stack' to avoid potential inlining. [Eric] net/openvswitch/actions.c | 23 +++++++++++------------ 1 file changed, 11 insertions(+), 12 deletions(-)