linux-kernel - Re: per-thread rusage

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Date:	Tue, 1 May 2007 21:57:25 -0700
From:	"Ulrich Drepper" <drepper@...il.com>
To:	"Theodore Tso" <tytso@....edu>,
	"Ulrich Drepper" <drepper@...il.com>,
	"Bill Irwin" <bill.irwin@...cle.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Eric Dumazet" <dada1@...mosbay.com>, linux-kernel@...r.kernel.org,
	wli@...omorphy.com
Subject: Re: per-thread rusage

On 5/1/07, Theodore Tso <tytso@....edu> wrote:
> The question is should we use setrlimit() to set the per-thread CPU
> limit, given that we would need some separate interface to set signal
> that should be sent.
>
> Is there any reason why we should have the interface specify whether
> the signal should be directed to a specified process or kernel
> thread-id, perhaps using si_pid field in the siginfo_t to specify
> which thread had exceeded its CPU limit.  Or would this be overkill?

The more I think about it the more complex it gets.  There is a
problem with delivering the signal to the receiving process itself: it
is out of time and cannot perform the cleanup operation anymore.  You
could grant it a grace period but how long should that be?  Some of
the cleanup handlers might take a long time.  If you don't enforce the
CPU limit then it doesn't have to be in the kernel and you might as
well use CLOCK_THREAD_CPUTIME_ID and create a timer.  This should
already work today.  If not it must be fixed.

Delivering the timeout signal to another thread isn't really possible
either since the cleanup code might access thread-local data which
wouldn't work since it's not the canceled thread's data which is
accessed.

I don't have a good answer right now whether enforced CPU limits can
be implemented at all.  But it seems for your purposes a timer with
the CPU clock might be sufficient.

> Do you think this is something that we could get standardized into an
> upcoming Posix/Posix Threads standard?

Regardless of whether a solution can be found, it's too late for the
next revision.  The deadline for new features is long gone by.
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