Re: [Lse-tech] RE: ext3 performance bottleneck as the number of s pindles gets large

From: Eric W. Biederman (
Date: Mon Jun 24 2002 - 12:14:08 EST

"Gross, Mark" <> writes:

> We are running the tests with the following mother board.
> cb2&
> Its a very nice box with 2 independent 64/66 PCI buses.
> Capable of 2x503MB/sec, using your logic ;)
> Regardless, the 640MB/s number was computed without considering the PCI bus
> limitations, or the dual port nature of the base 160MB/sec nature of the
> Adabptec SCSI-39160.
> -39160&cat=Products
> Realistically, we are looking for a max throughput of about 320MB/sec with 4
> adapters with enough drives attached.

Careful even with at 320MB/sec this requires 50% of your systems theoretical
memory bandwidth in DMA transfers.

Application level benchmarks like streams can only achieve memory copy numbers
on a PIII platform of about 320MB/sec. A highly tuned mmx, or sse memory
copy can do better but it is a challenge.

That close to the hardware limits finding the actual bottleneck can
get very tricky. At the very least I would run the system with
just one processor, and attempt to get the numbers that way. I can
trivially see spinlock hold times staying high simply because
the memory is busy with a DMA transfer, and so cannot be used to
transfer the new contents of the lock.

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This archive was generated by hypermail 2b29 : Sun Jun 30 2002 - 22:00:08 EST