Ian Godin <[EMAIL PROTECTED]> wrote: > > > I am trying to get very fast disk drive performance and I am seeing > some interesting bottlenecks. We are trying to get 800 MB/sec or more > (yes, that is megabytes per second). We are currently using > PCI-Express with a 16 drive raid card (SATA drives). We have achieved > that speed, but only through the SG (SCSI generic) driver. This is > running the stock 2.6.10 kernel. And the device is not mounted as a > file system. I also set the read ahead size on the device to 16KB > (which speeds things up a lot): > ... > samples % symbol name > 848185 8.3510 __copy_to_user_ll > 772172 7.6026 do_anonymous_page > 701579 6.9076 _spin_lock_irq > 579024 5.7009 __copy_user_intel > 361634 3.5606 _spin_lock > 343018 3.3773 _spin_lock_irqsave > 307462 3.0272 kmap_atomic > 193327 1.9035 page_fault
Something funny is happening here - it looks like there's plenty of CPU capacity left over. It's odd that you're getting a lot of pagefaults in this test but not with the sg_dd test, too. I wonder why dd is getting so many pagefaults? (I recall that sg_dd did something cheaty, but I forget what it was). Could you monitor the CPU load during the various tests? If the `dd' workload isn't pegging the CPU then it could be that there's something wrong with the I/O submission patterns. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
