Re: ppoll() stuck on POLLIN while TCP peer is sending

Eric Wong
2013-01-03T18:32:54Z

Eric Dumazet <eric.dumazet@gmail.com> wrote:
> On Wed, 2013-01-02 at 20:47 +0000, Eric Wong wrote:
> > Eric Wong <normalperson@yhbt.net> wrote:
> > > [1] my full setup is very strange.
> > >
> > > Other than the FUSE component I forgot to mention, little depends on
> > > the kernel. With all this, the standalone toosleepy can get stuck.
> > > I'll try to reproduce it with less...
> >
> > I just confirmed my toosleepy processes will get stuck while just
> > doing "rsync -a" between local disks. So this does not depend on
> > sendfile or FUSE to reproduce.
> > --
>
> How do you tell your 'toosleepy' is stuck ?

My original post showed it stuck with strace (in ppoll + send).
I only strace after seeing it's not using any CPU in top.

http://mid.gmane.org/20121228014503.GA5017@dcvr.yhbt.net
(lsof also confirmed the ppoll/send sockets were peers)

> If reading its output, you should change its logic, there is no
> guarantee the recv() will deliver exactly 16384 bytes each round.
>
> With the following patch, I cant reproduce the 'apparent stuck'

Right, the output is just an approximation and the logic there
was bogus.

Thanks for looking at this.