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Message-ID: <98df96d305081804061ea70686@mail.gmail.com>
Date: Thu, 18 Aug 2005 20:06:39 +0900
From: Hiro Yoshioka <lkml.hyoshiok@gmail.com>
Reply-To: hyoshiok@miraclelinux.com
To: Andi Kleen <ak@suse.de>
Subject: Re: [RFC] [PATCH] cache pollution aware __copy_from_user_ll()
Cc: Arjan van de Ven <arjan@infradead.org>, taka@valinux.co.jp,
       linux-kernel@vger.kernel.org, Hiro Yoshioka <hyoshiok@miraclelinux.com>
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On 16 Aug 2005 15:15:35 +0200, Andi Kleen <ak@suse.de> wrote:
> However it disables preemption, which especially for bigger
> copies will probably make the low latency people unhappy.

In the copy loop,
+#ifdef CONFIG_PREEMPT
+               if ( (i%64)==0 ) {
+                   MMX_RESTORE;
+                   MMX_SAVE;
+               };
+#endif

It costs several hundred clocks (wow) every 4KB copy.

It kills throughput but it makes the low latency people smile.

So I make two APIs. 
__copy_user_zeroing_nocache()
__copy_user_zeroing_inatomic_nocache()

The former is a low latency version and the other is a throughput version.

What do you think?

Regards,
  Hiro

-- 
Hiro Yoshioka
mailto:hyoshiok at miraclelinux.com