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

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Message-ID: <20100702112141.GJ10072@secunet.com>
Date:	Fri, 2 Jul 2010 13:21:41 +0200
From:	Steffen Klassert <steffen.klassert@...unet.com>
To:	Dan Kruchinin <dkruchinin@....org>
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 02, 2010 at 02:20:15PM +0400, Dan Kruchinin wrote:
> >
> > 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?
> 

Yes, the counters must accessed under lock. In the fastpath functions you 
hold the appropriate lock anyway. Modifying a local percpu value should
not be too painfull there.

The expensive thing is to access the percpu statistics, but this happens
on demand and is probaply a rare event.

Steffen
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