lkml.org 
[lkml]   [2009]   [May]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH RFC] perf_counter: Don't swap contexts containing locked mutex
Peter Zijlstra writes:

> > - && ctx1->parent_gen == ctx2->parent_gen;
> > + && ctx1->parent_gen == ctx2->parent_gen
> > + && ctx1->parent_gen != ~0ull;
> > }
>
> There's a nasty surprise for people a few generations down the line. All
> of a sudden performance drops for a while for some unknown reason, and
> then its good again,.. how odd ;-)

If you can add a counter every microsecond (which I don't think any
current processor can do) it'll still be more than half a million
years before we get that far...

> But yeah, seems fine, given that the alternative is yet another
> variable.

Actually, having a 1-bit flag might be cleaner since we can then just
clear it, rather than having to put the old parent_gen back.

> <snip all the other WARN_ON_ONCEs>
>
> How about:
>
> #define ASSERT_CTX_STABLE(ctx) \
> WARN_ON_ONCE((ctx)->parent_gen != ~0ull || ctx->parent_ctx)
>
> which would deal with both a 'locked' context and uncloned one?

Yeah, all right.

> Could we maybe write this as:
>
> static struct perf_counter_ctx *pin_ctx(struct perf_counter *counter, u64 *old_gen)

Yep, good idea.

Paul.


\
 
 \ /
  Last update: 2009-05-29 10:27    [W:0.075 / U:3.952 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site