Messages in this thread | | | Date | Wed, 31 Aug 2005 09:16:59 -0600 | From | jmerkey <> | Subject | Re: Where is the performance bottleneck? |
| |
I have seen an 80GB/sec limitation in the kernel unless this value is changed in the SCSI I/O layer for 3Ware and other controllers during testing of 2.6.X series kernels.
Change these values in include/linux/blkdev.h and performance goes from 80MB/S to over 670MB/S on the 3Ware controller.
//#define BLKDEV_MIN_RQ 4 //#define BLKDEV_MAX_RQ 128 /* Default maximum */ #define BLKDEV_MIN_RQ 4096 #define BLKDEV_MAX_RQ 8192 /* Default maximum */
Jeff
Jens Axboe wrote:
>On Wed, Aug 31 2005, Holger Kiehl wrote: > > >>On Wed, 31 Aug 2005, Jens Axboe wrote: >> >> >> >>>Nothing sticks out here either. There's plenty of idle time. It smells >>>like a driver issue. Can you try the same dd test, but read from the >>>drives instead? Use a bigger blocksize here, 128 or 256k. >>> >>> >>> >>I used the following command reading from all 8 disks in parallel: >> >> dd if=/dev/sd?1 of=/dev/null bs=256k count=78125 >> >>Here vmstat output (I just cut something out in the middle): >> >>procs -----------memory---------- ---swap-- -----io---- --system-- >>----cpu----^M >> r b swpd free buff cache si so bi bo in cs us sy id >> wa^M >> 3 7 4348 42640 7799984 9612 0 0 322816 0 3532 4987 0 22 >> 0 78 >> 1 7 4348 42136 7800624 9584 0 0 322176 0 3526 4987 0 23 >> 4 74 >> 0 8 4348 39912 7802648 9668 0 0 322176 0 3525 4955 0 22 >> 12 66 >> 1 7 4348 38912 7803700 9636 0 0 322432 0 3526 5078 0 23 >> >> > >Ok, so that's somewhat better than the writes but still off from what >the individual drives can do in total. > > > >>>You might want to try the same with direct io, just to eliminate the >>>costly user copy. I don't expect it to make much of a difference though, >>>feels like the problem is elsewhere (driver, most likely). >>> >>> >>> >>Sorry, I don't know how to do this. Do you mean using a C program >>that sets some flag to do direct io, or how can I do that? >> >> > >I've attached a little sample for you, just run ala > ># ./oread /dev/sdX > >and it will read 128k chunks direct from that device. Run on the same >drives as above, reply with the vmstat info again. > > > >------------------------------------------------------------------------ > >#include <stdio.h> >#include <stdlib.h> >#define __USE_GNU >#include <fcntl.h> >#include <stdlib.h> >#include <unistd.h> > >#define BS (131072) >#define ALIGN(buf) (char *) (((unsigned long) (buf) + 4095) & ~(4095)) >#define BLOCKS (8192) > >int main(int argc, char *argv[]) >{ > char *p; > int fd, i; > > if (argc < 2) { > printf("%s: <dev>\n", argv[0]); > return 1; > } > > fd = open(argv[1], O_RDONLY | O_DIRECT); > if (fd == -1) { > perror("open"); > return 1; > } > > p = ALIGN(malloc(BS + 4095)); > for (i = 0; i < BLOCKS; i++) { > int r = read(fd, p, BS); > > if (r == BS) > continue; > else { > if (r == -1) > perror("read"); > > break; > } > } > > return 0; >} > >
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |