netdev - Re: [PATCH net-next v2] openvswitch: reduce stack usage in do_execute

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Message-ID: <EFA8E5B7-948A-48C7-A52F-DDA00B0A2EE3@redhat.com>
Date: Fri, 22 Sep 2023 08:43:32 +0200
From: Eelco Chaudron <echaudro@...hat.com>
To: netdev@...r.kernel.org
Subject: Re: [PATCH net-next v2] openvswitch: reduce stack usage in
 do_execute_actions



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@....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@...hat.com