From: Waiman Long <longman@redhat.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Alexey Dobriyan <adobriyan@gmail.com>,
Kees Cook <keescook@chromium.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
Davidlohr Bueso <dave@stgolabs.net>,
Miklos Szeredi <miklos@szeredi.hu>,
Daniel Colascione <dancol@google.com>,
Dave Chinner <david@fromorbit.com>,
Randy Dunlap <rdunlap@infradead.org>
Subject: Re: [PATCH v2 0/4] /proc/stat: Reduce irqs counting performance overhead
Date: Wed, 9 Jan 2019 15:14:38 -0500 [thread overview]
Message-ID: <492604fe-a7d6-fdfe-6a8b-77423a739644@redhat.com> (raw)
Message-ID: <20190109201438.WhdG_e3AcmW8xjgrzi6AdNROe8kP5TSw-d3TstuEC2A@z> (raw)
In-Reply-To: <20190109195944.GQ6310@bombadil.infradead.org>
On 01/09/2019 02:59 PM, Matthew Wilcox wrote:
> On Wed, Jan 09, 2019 at 01:54:36PM -0500, Waiman Long wrote:
>> If you read patch 4, you can see that quite a bit of CPU cycles was
>> spent looking up the radix tree to locate the IRQ descriptor for each of
>> the interrupts. Those overhead will still be there even if I use percpu
>> counters. So using percpu counter alone won't be as performant as this
>> patch or my previous v1 patch.
> Hm, if that's the overhead, then the radix tree (and the XArray) have
> APIs that can reduce that overhead. Right now, there's only one caller
> of kstat_irqs_usr() (the proc code). If we change that to fill an array
> instead of returning a single value, it can look something like this:
>
> void kstat_irqs_usr(unsigned int *sums)
> {
> XA_STATE(xas, &irq_descs, 0);
> struct irq_desc *desc;
>
> xas_for_each(&xas, desc, ULONG_MAX) {
> unsigned int sum = 0;
>
> if (!desc->kstat_irqs)
> continue;
> for_each_possible_cpu(cpu)
> sum += *per_cpu_ptr(desc->kstat_irqs, cpu);
>
> sums[xas->xa_index] = sum;
> }
> }
OK, I will try something like that as a replacement of patch 4 to see
how it compares with my current patch.
Thanks,
Longman
next prev parent reply other threads:[~2019-01-09 20:14 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-09 17:23 [PATCH v2 0/4] /proc/stat: Reduce irqs counting performance overhead Waiman Long
2019-01-09 17:23 ` [PATCH v2 1/4] /proc/stat: Extract irqs counting code into show_stat_irqs() Waiman Long
2019-01-09 17:23 ` [PATCH v2 2/4] /proc/stat: Only do percpu sum of active IRQs Waiman Long
2019-01-09 17:23 ` [PATCH v2 3/4] genirq: Track the number " Waiman Long
2019-01-09 17:23 ` [PATCH v2 4/4] /proc/stat: Call kstat_irqs_usr() only for " Waiman Long
2019-01-09 17:23 ` Waiman Long
2019-01-09 17:39 ` Waiman Long
2019-01-09 17:44 ` [PATCH v2 0/4] /proc/stat: Reduce irqs counting performance overhead Matthew Wilcox
2019-01-09 18:03 ` Waiman Long
2019-01-09 18:24 ` Matthew Wilcox
2019-01-09 18:37 ` Waiman Long
2019-01-09 18:52 ` Matthew Wilcox
2019-01-09 18:57 ` Waiman Long
2019-01-09 18:54 ` Waiman Long
2019-01-09 19:59 ` Matthew Wilcox
2019-01-09 19:59 ` Matthew Wilcox
2019-01-09 20:14 ` Waiman Long [this message]
2019-01-09 20:14 ` Waiman Long
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