Messages in this thread | | | Date | Wed, 8 May 2002 21:16:30 -0700 (PDT) | From | Andre Hedrick <> | Subject | Re: [PATCH] 2.5.14 IDE 56 |
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Lincoln,
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 ...
On Thu, 9 May 2002, Lincoln Dale wrote:
> At 01:42 PM 8/05/2002 +0100, Alan Cox wrote: > >The SCSI layer is significant overhead even in 2.5. > > i did some benchmarking on a high-end dual P3 Xeon (Serverworks chipset ) > with QLogic 2300 (2gbit/s) 64/66 Fibre Channel controllers. > > using the '/dev/sgX' interface to issue scsi reads/writes allowed me to hit > the magical limit of 200mbyte/sec throughput. (basically just about > linerate). (simultaneous "sg_read if=/dev/sgX mmap=1 bs=512 count=35M"; > sg_read from the sg-tools package) > > doing the same test thru the block-layer was basically capped at around > 135mbyte/sec. (simultaneous "dd if=/dev/sdX of=/dev/null bs=512 count=35M"). > > whether the bottleneck was copy-from-kernel-to-userspace (ie. exhaustion of > Front-Side-Bus / memory bandwidth) or related to block-layer overhead and > scsi layer overheads, i haven't yet validated, but at a ~35% performance > difference is relatively significant nontheless. > > cpu utlization on the sg interface was under 10%. using 'dd' on the sd > interface, both gigahertz P3 Xeons had 0% idle time. > > > cheers, > > lincoln. > > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >
Andre Hedrick LAD Storage Consulting Group
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