Re: [lkml] RE: self piping and context switching

[Iker <iker@computer.org>]

More specifically, I was wondering if the write to the pipe or the call back
into poll involved anything that might prompt the scheduler to replace the
thread in this scenario.

> It's reasonable to expect that this will be the most common case and the
> one to optimize. It is unreasonable to fail if this doesn't happen, since
> it's not guaranteed to happen. Note that if by "without a context switch"
> you really mean without another thread getting a chance to run, then it is
> totally unreasonable.

Are you referring to transitions to/from kernel space? If so, wouldn't the
write
on the pipe and the call to poll both result in transitions?

Regards,
Iker


----- Original Message -----
From: "David Schwartz" <davids@webmaster.com>
To: "Iker" <iker@computer.org>; <linux-kernel@vger.kernel.org>
Sent: Friday, September 12, 2003 10:04 PM
Subject: [lkml] RE: self piping and context switching


>
> > Assume a thread is monitoring a set of fd's which include both ends of
> > a pipe (using poll, for example). If the thread writes to the pipe (in
> > order to notify itself for whatever reason) is it reasonable to expect
> > that it will be able to return to its poll loop and get the event
> > without a context switch? (provided it quickly returns to the poll
> > loop).
>
> It's reasonable to expect that this will be the most common case and the
> one to optimize. It is unreasonable to fail if this doesn't happen, since
> it's not guaranteed to happen. Note that if by "without a context switch"
> you really mean without another thread getting a chance to run, then it is
> totally unreasonable. On SMP systems and with hyper-threading, threads can
> run concurrently.
>
> DS
>
>
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