linux-kernel - Re: [patch V2 00/20] timer: Refactor the timer wheel

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Date:	Wed, 22 Jun 2016 10:44:19 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Mike Galbraith <umgwanakikbuti@...il.com>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Chris Mason <clm@...com>,
	Arjan van de Ven <arjan@...radead.org>, rt@...utronix.de,
	Rik van Riel <riel@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	George Spelvin <linux@...encehorizons.net>,
	Len Brown <lenb@...nel.org>, ltp@...ts.linux.it
Subject: Re: [patch V2 00/20] timer: Refactor the timer wheel

B1;2802;0cOn Wed, 22 Jun 2016, Mike Galbraith wrote:
> FWIW, testing with ltp, I noticed a new failure in logs.  It turns out
> to be intermittent, but the testcase mostly fails.

You forgot to cc the LTP folks ...
 
> rtbox:~ # /usr/local/ltp/conformance/interfaces/sigtimedwait/sigtimedwait_1-1.run-test
> Test FAILED: sigtimedwait() did not return in the required time
> time_elapsed: 1.197057
> ...come on, you can do it...
> rtbox:~ # /usr/local/ltp/conformance/interfaces/sigtimedwait/sigtimedwait_1-1.run-test
> Test PASSED
> 
> #define ERRORMARGIN 0.1
> ...
>         if ((time_elapsed > SIGTIMEDWAITSEC + ERRORMARGIN)
>             || (time_elapsed < SIGTIMEDWAITSEC - ERRORMARGIN)) {
>                 printf("Test FAILED: sigtimedwait() did not return in "
>                         "the required time\n");
>                 printf("time_elapsed: %lf\n", time_elapsed);
>                 return PTS_FAIL;
>         }
> 
> Looks hohum to me, but gripe did arrive with patch set, so you get a note.

hohum is a euphemism. That's completely bogus.

The only guarantee a syscall with timers has is: timer does not fire early.

Thanks,

	tglx