Messages in this thread |  | | Subject | Re: Early SPECWeb99 results on 2.5.33 with TSO on e1000 | From | (Eric W. Biederman) | Date | 11 Sep 2002 09:31:53 -0600 |
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"David S. Miller" <davem@redhat.com> writes:
> From: ebiederm@xmission.com (Eric W. Biederman) > Date: 11 Sep 2002 09:06:36 -0600 > > "Martin J. Bligh" <mbligh@aracnet.com> writes: > > > We can push about 420MB/s of IO out of this thing (out of that > > theoretical 800Mb/s). > > Sounds about average for a P3. I have pushed the full 800MiB/s out of > a P3 processor to memory but it was a very optimized loop. > > You pushed that over the PCI bus of your P3? Just to RAM > doesn't count, lots of cpu's can do that. > > That's what makes his number interesting.
I agree. Getting 420MB/s to the pci bus is nice, especially with a P3. The 800MB/s to memory was just the test I happened to conduct about 2 years ago when I was still messing with slow P3 systems. It was a proof of concept test to see if we could plug in an I/O card into a memory slot.
On a current P4 system with the E7500 chipset this kind of thing is easy. I have gotten roughly 450MB/s to a single myrinet card. And there is enough theoretical bandwidth to do 4 times that. I haven't had a chance to get it working in practice. When I attempted to run to gige cards simultaneously I had some weird problem (probably interrupt related) where adding additional pci cards did not deliver any extra performance.
On a P3 to get writes from the cpu to hit 800MB/s you use the special cpu instructions that bypass the cache.
My point was that I have tested the P3 bus in question and I achieved a real world 800MB/s over it. So I expect that on the system in question unless another bottleneck is hit, it should be possible to achieve a real world 800MB/s of I/O. There are enough pci busses to support that kind of traffic.
Unless the memory controller is carefully placed on the system though doing 400+MB/s could easily eat up most of the available memory bandwidth and reduce the system to doing some very slow cache line fills.
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