Re: [PATCH RFC] time: drop do_sys_times spinlock

Rik van Riel
2014-08-13T13:24:42Z

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 08/13/2014 07:11 AM, Peter Zijlstra wrote:
> On Wed, Aug 13, 2014 at 08:59:50AM +0200, Mike Galbraith wrote:
>
>> I was told that clock_gettime(CLOCK_PROCESS_CPUTIME_ID) has
>> scalability issues on BIG boxen
>
>> I'm sure the real clock_gettime() using proggy that gummed up a
>> ~1200 core box for "a while" wasn't the testcase below, which
>> will gum it up for a long while, but looks to me like using
>> CLOCK_PROCESS_CPUTIME_ID from LOTS of threads is a "Don't do
>> that, it'll hurt a LOT".
>
> Yes, don't do that. Its unavoidably slow and bad.

I don't see why that needs the tasklist_lock, when do_sys_times
grabs a different lock.

If the same bottleneck exists from multiple places, maybe it does
make sense to have a seqlock for the statistics at the sighand
level?

I can code up a patch that does that, and throw it over the wall
to people with big systems who hit that bottleneck on a regular
basis...

- --
All rights reversed
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1

iQEcBAEBAgAGBQJT62b2AAoJEM553pKExN6DBJ4H/AyVsN4N73Gp/wrm7waaNjpS
kU5R2pIGzJqxJ4BZi+aeiuT09ZoSHCl3nvSsMNBm712NX1jyFVC4I91ON18tsB3o
P/tipcCP9Q6QSW8+lPRNz459OsaXX+wyRxcdnUtZN7SVb+NTWlxZ4o8UiVljZYSV
2mRr2ipd/0vKn7J9twaIP0UMddTpIrnMTCMKookoWXoHeJIXsYAs3XTRsoPJAddz
0ba5H7OGjphOSCyMkDDo3GG+K8oHJIpD8PHT38pXfX+suNEGxMO7PGvvEyUcrJKx
5355fnU6/1mksPlRD5DIwMowMjbY5zy71P8Lv4Eg+LY+C/kGjyrz9Maa0SyRMh8=
=VQ/m
-----END PGP SIGNATURE-----