Re: [RFC PATCH] net/core: use wake_up_interruptible_poll() in sock_def_readable()

[Jiayuan Chen <jiayuan.chen@linux.dev>]

On 5/26/26 2:36 PM, Xuewen Yan wrote:
> sock_def_readable() currently uses wake_up_interruptible_sync_poll() to
> wake up tasks waiting for readable data on a socket. The _sync variant
> sets the WF_SYNC flag, which tells the scheduler that the waker will
> schedule away soon, so the wakee should stay on the same CPU to avoid
> needless cache bouncing.
>
> However, we found that the following stack:
>   -vfs_write
>   -sock_write_iter
>   -unix_stream_sendmsg
>   -sock_def_readable
>   -__wake_up_sync_key
>
> In this process-context scenario, the waker does NOT go to sleep
> after the wakeup. With WF_SYNC, the scheduler is misled into placing
> the wakee on the waker's CPU (via wake_affine_idle()'s sync path when
> nr_running == 1), causing both the sender and receiver to contend for
> the same CPU. This may hurt throughput for IPC workloads on multi-core
> systems where the sender and receiver could otherwise run in parallel
> on different CPUs.


WF_SYNC isn't a hard binding.

What's your test environment and benchmark ?