Messages in this thread | | | Date | Sun, 17 Feb 2008 22:18:10 +0100 | From | Willy Tarreau <> | Subject | [PATCH 0/2] libata: implement 32-bit transfers for PIO mode |
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Hi Jeff,
For several times I tried libata on small machines equipped with either CompactFlash or IDE DOM (Disk-On-Module). All those machines with small flashes (<= 256 MB) were about 35-40% slower under libata than under the plain old IDE driver. I realized that all the slower ones were running PIO only.
Today I had time to investigate the issue on a Geode LX board. At first I thought it was the pata_cs5536 driver which would have incorrect timings, but this was not the case. I finally noticed that under IDE, my flashes were running in 32-bit mode while I could not enable 32-bit with libata.
Reading ata_data_xfer() made it obvious that transfers were only 16-bit wide.
Thus, I have implemented the 32-bit mode to bring the performance back to the level of the old IDE driver. I jumped from 1.5 MB/s to 2.5 MB/s, which is an important difference at this level of performance, especially when large files are read. The 32-bit mode is enabled using the ioctl which is already implemented but only accepts a null value.
I'm joining two patches which I hope you'll consider for inclusion. I've updated them to latest Linus' git.
Best regards, Willy
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