Re: High 50us+ latencies in the process signal handling path

[ankita@in.ibm.com (Ankita Garg)]

Hi,

On Thu, Oct 18, 2007 at 11:36:18AM -0400, Luis Claudio R. Goncalves wrote:
> Ankita,
> 
> On Thu, Oct 18, 2007 at 06:56:14PM +0530, Ankita Garg wrote:
> | Hi David,
> | 
> | On Thu, Oct 18, 2007 at 05:52:42AM -0700, David Miller wrote:
> | > From: ankita@in.ibm.com (Ankita Garg)
> | > Date: Thu, 18 Oct 2007 18:18:27 +0530
> | > 
> | > > Any thoughts on where in the code could these large latencies be
> | > > attributed to?
> | > 
> | > If the max latency is usually the first one, it's could be the page
> | > fault the signal handler is taking the first time it is executed.
> | 
> | Thanks for looking into this. Attaching the entire log from the testrun.
> | It indicates that in each run of the 10000 iterations, there are about 100+
> | failures, with large iterations. Also, on intrumenting the testcode to
> | find out the iterations which see large latencies, I see that as the
> | number of iterations increase, the latencies increase.
> 
> You might wanna check signaltest:
> 
> git clone git://git.kernel.org/pub/scm/linux/kernel/git/tglx/rt-tests.git rt-tests
>

Are any previous logs available for signaltest? This is what I get on 2.6.23-rt1-

# ./signaltest -q -p 85 -l100000 -t8
T: 0 ( 6791) P:85 C: 100000 Min:    109 Act:  148 Avg:  143 Max:     252
T: 1 ( 6792) P:85 C: 100000 Min:    109 Act:  148 Avg:  769 Max:   10240
T: 2 ( 6793) P:85 C: 100000 Min:    109 Act:  148 Avg:  769 Max:   10247
T: 3 ( 6794) P:85 C: 100000 Min:    109 Act:  161 Avg:  769 Max:   10238
T: 4 ( 6795) P:85 C: 100000 Min:    109 Act:  183 Avg:  769 Max:   10238
T: 5 ( 6796) P:85 C: 100000 Min:    109 Act:  214 Avg:  769 Max:   10239
T: 6 ( 6797) P:85 C: 100000 Min:    109 Act:  236 Avg:  769 Max:   10237
T: 7 ( 6798) P:85 C: 100000 Min:    109 Act:  329 Avg:  769 Max:   10238

And this on 2.6.21.4-rt10-

# ./signaltest -q -p 85 -l100000 -t8
T: 0 ( 3767) P:85 C: 100000 Min:     56 Act:  101 Avg:   99 Max:     162
T: 1 ( 3768) P:85 C: 100000 Min:     56 Act:  101 Avg:  725 Max:   10164
T: 2 ( 3769) P:85 C: 100000 Min:     56 Act:  101 Avg:  725 Max:   10164
T: 3 ( 3770) P:85 C: 100000 Min:     56 Act:  102 Avg:  725 Max:   10164
T: 4 ( 3771) P:85 C: 100000 Min:     56 Act:  111 Avg:  725 Max:   10165
T: 5 ( 3772) P:85 C: 100000 Min:     56 Act:  120 Avg:  725 Max:   10163
T: 6 ( 3773) P:85 C: 100000 Min:     56 Act:  135 Avg:  725 Max:   10164
T: 7 ( 3774) P:85 C: 100000 Min:     56 Act:  178 Avg:  725 Max:   10165

The values seem rather high!
 
> Regards,
> Luis
> -- 
> [ Luis Claudio R. Goncalves                    Bass - Gospel - RT ]
> [ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9  2696 7203 D980 A448 C8F8 ]
> 
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-- 
Regards,
Ankita Garg (ankita@in.ibm.com)
Linux Technology Center
IBM India Systems & Technology Labs, 
Bangalore, India