Re: [PATCH v3] tcp: add support for SO_PEEK_OFF

On 2024-02-15 12:46, Eric Dumazet wrote:

On Thu, Feb 15, 2024 at 6:41 PM Paolo Abeni wrote:

...

Note: please send text-only email to netdev.

On Thu, 2024-02-15 at 10:11 -0500, Jon Maloy wrote:

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I wonder if the following could be acceptable:

if (flags & MSG_PEEK) sk_peek_offset_fwd(sk, used); else if (peek_offset > 0) sk_peek_offset_bwd(sk, used);

peek_offset is already present in the data cache, and if it has the value zero it means either that that sk->sk_peek_off is unused (-1) or actually is zero. Either way, no rewind is needed in that case. I agree the above should avoid touching cold cachelines in the fastpath, and looks functionally correct to me.

The last word is up to Eric :)

An actual patch seems needed.

In the current form, local variable peek_offset is 0 when !MSG_PEEK.

So the "else if (peek_offset > 0)" would always be false.

Yes, of course. This wouldn't work unless we read sk->sk_peek_off at the beginning of the function. I will look at the other suggestions. ///jon