Message-ID: <43D9E15B.9000407@cosmosbay.com>
Date: Fri, 27 Jan 2006 10:01:15 +0100
From: Eric Dumazet <dada1@cosmosbay.com>
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To: Ravikiran G Thirumalai <kiran@scalex86.org>
CC: Andrew Morton <akpm@osdl.org>, davem@davemloft.net,
       linux-kernel@vger.kernel.org, shai@scalex86.org, netdev@vger.kernel.org,
       pravins@calsoftinc.com
Subject: Re: [patch 2/4] net: Percpufy frequently used variables -- struct
 proto.memory_allocated
References: <20060126185649.GB3651@localhost.localdomain> <20060126190212.GD3651@localhost.localdomain>
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Ravikiran G Thirumalai a ?crit :
> Change struct proto->memory_allocated to a batching per-CPU counter 
> (percpu_counter) from an atomic_t.  A batching counter is better than a 
> plain per-CPU counter as this field is read often.
> 
> Signed-off-by: Pravin B. Shelar <pravins@calsoftinc.com>
> Signed-off-by: Ravikiran Thirumalai <kiran@scalex86.org>
> Signed-off-by: Shai Fultheim <shai@scalex86.org>
> 

Hello Ravikiran

I like this patch, but I'm not sure current percpu_counter fits the needs.

The percpu_counter_read() can return a value that is off by +-
FBC_BATCH*NR_CPUS, ie 2*(NR_CPUS^2) or 4*(NR_CPUS^2)

if NR_CPUS = 128, the 'error' from percpu_counter_read() is +- 32768

Is it acceptable ?

Thank you
Eric
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