Messages in this thread | | | Date | Tue, 30 Mar 2004 10:31:08 -0500 | From | Jeff Garzik <> | Subject | Re: [PATCH] speed up SATA |
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Marc Bevand wrote: > Jeff Garzik wrote: > >> >> [...] >> With this simple patch, the max request size goes from 128K to 32MB... >> so you can imagine this will definitely help performance. Throughput >> goes up. Interrupts go down. Fun for the whole family. >> [...] > > > I have experienced a noticeable improvement concerning the CPU usage > and disk throughput with this patch. > > Benchmark specs: > > o read from only 1 disk (sda), or from 2 disks (sda+sdb), with > 1 or 2 instances of "dd if=/dev/sd? of=/dev/null bs=100M". > o hardware: two Seagate 160GB SATA, on a Silicon Image 3114, on a > 32-bit/33MHz PCI bus, 1GB RAM. > o software: kernel 2.6.5-rc2-bk6-libata2.
[...]
Very cool, thanks for benching!
> As other people were complaining that the 32MB max request size might be > too > high, I did give a try to 1MB (by replacing "65534" by "2046" in the > patch). > There is no visible differences between 32MB and 1MB.
This is not surprising, since: * the scatter-gather table imposes a limit of 8MB * the VM further imposes limits on readahead and writeback
So 32MB is the hardware max, but not really achieveable due to other factors.
> PS: Jeff: "pci_dma_mapping_error()", in libata-core.c from your latest > 2.6-libata patch, is an unresolved symbol. I have had to comment it out > to be able to compile the kernel.
Yeah, this is only found in the bleeding-edge-latest 2.6.x kernels. You did the right thing...
Regards,
Jeff
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