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Date: Tue, 17 Aug 2004 09:48:26 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Lee Revell <rlrevell@joe-job.com>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
       Felipe Alfaro Solana <felipe_alfaro@linuxmail.org>,
       Florian Schmidt <mista.tapas@gmx.net>, tytso@mit.edu
Subject: Re: [patch] Latency Tracer, voluntary-preempt-2.6.8-rc4-O6
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References: <20040726204720.GA26561@elte.hu> <20040729222657.GA10449@elte.hu> <20040801193043.GA20277@elte.hu> <20040809104649.GA13299@elte.hu> <20040810132654.GA28915@elte.hu> <20040812235116.GA27838@elte.hu> <1092374851.3450.13.camel@mindpipe> <1092375673.3450.15.camel@mindpipe> <20040813103151.GH8135@elte.hu> <1092699974.13981.95.camel@krustophenia.net>
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* Lee Revell <rlrevell@joe-job.com> wrote:

> I have attached a patch that effectively disables extract_entropy.  I
> am adding Theodore T'so to the cc: list as he is the author of the
> code in question.
> 
> For the time being this hack is required to avoid ~0.5 ms
> non-preemptible sections caused by the excessive memcpy's in
> extract_entropy.

i'm not 100% sure it's the memcpy's - but it's extract_entropy()
overhead. Might be the algorithmic slowness of SHATransform().

> +	return nbytes;
> +    

since this effectively disables the random driver i cannot add it to the
patch.

there's another thing you could try: various SHA_CODE_SIZE values in
drivers/char/random.c. Could you try 1, 2 and 3, does it change the
overhead as seen in the trace?

	Ingo