On 12/21, Song Liu wrote:
On Thu, Dec 17, 2020 at 9:24 AM Stanislav Fomichev <sdf@xxxxxxxxxx> wrote:
>
> When we attach a bpf program to cgroup/getsockopt any other getsockopt()
> syscall starts incurring kzalloc/kfree cost. While, in general, it's
> not an issue, sometimes it is, like in the case of TCP_ZEROCOPY_RECEIVE.
> TCP_ZEROCOPY_RECEIVE (ab)uses getsockopt system call to implement
> fastpath for incoming TCP, we don't want to have extra allocations in
> there.
>
> Let add a small buffer on the stack and use it for small (majority)
> {s,g}etsockopt values. I've started with 128 bytes to cover
> the options we care about (TCP_ZEROCOPY_RECEIVE which is 32 bytes
> currently, with some planned extension to 64 + some headroom
> for the future).
>
> It seems natural to do the same for setsockopt, but it's a bit more
> involved when the BPF program modifies the data (where we have to
> kmalloc). The assumption is that for the majority of setsockopt
> calls (which are doing pure BPF options or apply policy) this
> will bring some benefit as well.
>
> Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
Could you please share some performance numbers for this optimization?
We've found out about this problem by looking at our global google
profiler, where TCP_ZEROCOPY_RECEIVE was showing up higher than usual.
So I don't really have a nice reproducer, but I would assume I can try
to run something like tools/testing/selftests/net/tcp_mmap.c under perf
and see if there is a clear difference.
