lkml.org 
[lkml]   [2019]   [May]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2] locking/lock_events: Use this_cpu_add() when necessary
On Fri, May 24, 2019 at 02:11:23PM -0400, Waiman Long wrote:
> On 5/24/19 1:39 PM, Will Deacon wrote:
>
> And the whole "not precise" thing should be documented, of course.
>
> Yes, I will update the patch to document that fact that the count may
> not be precise. Anyway even if we have a 1-2% error, it is not a big
> deal in term of presenting a global picture of what operations are being
> done.
>
> I suppose one alternative would be to have a per-cpu local_t variable,
> and do the increments on that. However, that's probably worse than the
> current approach for x86.
>
> I don't quite understand what you mean by per-cpu local_t variable. A per-cpu
> variable is either statically allocated or dynamically allocated. Even with
> dynamical allocation, the same problem exists, I think unless you differentiate
> between irq context and process context. That will make it a lot more messier,
> I think.

So I haven't actually tried this to see if it works, but all I meant was
that you could replace the current:

DECLARE_PER_CPU(unsigned long, lockevents[lockevent_num]);

with:

DECLARE_PER_CPU(local_t, lockevents[lockevent_num]);

and then rework the inc/add macros to use a combination of raw_cpu_ptr
and local_inc().

I think that would allow you to get rid of the #ifdeffery, but it may
introduce a small overhead for x86.

Will

\
 
 \ /
  Last update: 2019-05-24 20:33    [W:0.041 / U:0.512 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site