linux-kernel - Re: [PATCH 2/2] pcrypt: sysfs interface

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Message-ID: <AANLkTinFqMtdfvbYDIGjQHoWa3dmUuruTvxG-upUU-7S@mail.gmail.com>
Date:	Fri, 2 Jul 2010 14:20:15 +0400
From:	Dan Kruchinin <dkruchinin@....org>
To:	Steffen Klassert <steffen.klassert@...unet.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [PATCH 2/2] pcrypt: sysfs interface

On Fri, Jul 2, 2010 at 1:08 PM, Steffen Klassert
<steffen.klassert@...unet.com> wrote:
> On Thu, Jul 01, 2010 at 06:28:34PM +0400, Dan Kruchinin wrote:
>> >
>> > These statistic counters add a lot of atomic operations to the fast-path.
>> > Would'nt it be better to have these statistics in a percpu manner?
>> > This would avoid the atomic operations and we would get some additional
>> > information on the distribution of the queued objects.
>> >
>>
>> If I understood you correctly the resulting sysfs hierarchy would look like
>> this one:
>> pcrypt/
>> |- serial_cpumask
>> |- parallel_cpumask
>> |- w0/
>> +--- parallel_objects
>> +--- serial_objects
>> +--- reorder_objects
>> |- w1/
>> ...
>> |- wN/
>>
>> right? If so I think it won't be very convenient to monitor summary number
>> of parallel, serial and reorder objects.
>
> Yes, I thought about something like this. You can still take the sum
> over the percpu objects when you output the statistics.

But summation can not be clear without some kind of lock because
while we're summing another CPU can increase or decrease its percpu statistic
counters. Then each statistic percpu counter must be modified under lock, right?

>
>
>> Anyway I think these atomic operations take very small time in comparison
>> with other operations in padata. So small that it can be ignored.
>
> I have a patch in queue that simplifies the serialization mechanism and
> reduces the accesses of foreign and global memory as much as possible
> in the parallel codepath. Adding atomic operations to global memory
> (just to collect statistics) to the parallel codepath would go in the
> opposite direction.
>
> Steffen
>



-- 
W.B.R.
Dan Kruchinin
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