Re: [PATCH] 2.5.14 IDE 56

From: Alan Cox (alan@lxorguk.ukuu.org.uk)
Date: Thu May 09 2002 - 08:32:09 EST


> You are right on the money!
> There is about 35-40% throughput killjoy "copy-from-kernel-to-userspace".
> It is easy to demo if you have a bus analizer and can do accounting on the
> data io less the command block overhead.
>
> CR3's are your friend, not ...

You should be able to verify that by using large O_DIRECT I/O's. The
block layer itself may well be part of the overhead. With the scsi layer,
the block->scsi handling code is definitely a bottleneck to performance
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