Re: [PATCH 0/2] /proc/stat: Reduce irqs counting performance overhead

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 01/07/2019 05:32 PM, Dave Chinner wrote:
> On Mon, Jan 07, 2019 at 10:12:56AM -0500, Waiman Long wrote:
>> As newer systems have more and more IRQs and CPUs available in their
>> system, the performance of reading /proc/stat frequently is getting
>> worse and worse.
> Because the "roll-your-own" per-cpu counter implementaiton has been
> optimised for low possible addition overhead on the premise that
> summing the counters is rare and isn't a performance issue. This
> patchset is a direct indication that this "summing is rare and can
> be slow" premise is now invalid.
>
> We have percpu counter infrastructure that trades off a small amount
> of addition overhead for zero-cost reading of the counter value.
> i.e. why not just convert this whole mess to percpu_counters and
> then just use percpu_counter_read_positive()? Then we just don't
> care how often userspace reads the /proc file because there is no
> summing involved at all...
>
> Cheers,
>
> Dave.

Yes, percpu_counter_read_positive() is cheap. However, you still need to
pay the price somewhere. In the case of percpu_counter, the update is
more expensive.

I would say the percentage of applications that will hit this problem is
small. But for them, this problem has some significant performance overhead.

Cheers,
Longman





[Index of Archives]     [Linux Ext4 Filesystem]     [Union Filesystem]     [Filesystem Testing]     [Ceph Users]     [Ecryptfs]     [AutoFS]     [Kernel Newbies]     [Share Photos]     [Security]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux Cachefs]     [Reiser Filesystem]     [Linux RAID]     [Samba]     [Device Mapper]     [CEPH Development]

  Powered by Linux