Re: [linux-next:master] [pipe_read] aaec5a95d5: stress-ng.poll.ops_per_sec 11.1% regression

[Oleg Nesterov <oleg@redhat.com>]

Forgot to mention...

On 01/20, Oleg Nesterov wrote:
>
> On 01/20, Mateusz Guzik wrote:
> >
> > Whatever the long term fate of the patch I think it would be prudent to
> > skip it in this merge window.
>
> Perhaps... I'll try to take another look tomorrow.
>
> Just one note right now.
>
> > First two notes:
> > 1. the change only considers performing a wake up if the current
> > source buf got depleted -- if there is a blocked writer and there is at
> > least one byte in the current buf nothing happens, which is where the
> > difference in results is coming from
>
> Sorry I don't understand. Unless this patch is buggy, pipe_read() must
> always wakeup a blocked writer if the writer can write at least one byte.
>
> The writer can't write to "current" buf = pipe->bufs[tail & mask] if
> pipe_full() is still true.

But I'll recheck this logic once again tomorrow, perhaps I misread
pipe_write() when I made this patch.

Oleg.