2012/7/15 majianpeng <majianpeng@xxxxxxxxx>: > Create a raid5 using four disk and the chunksize is 512K. > Test command is: dd if=/dev/zero of=/dev/md0 bs=1536K count=90000 oflag=direct > > In RHEL6(kernel 2.6.32):speed about 240MB/s > In 3.5.0-rc5:speed about 77MB/S > Add two patch in 3.5.0-rc5, speed about 200MB/S. > > So the performance of odirect-wrirte for block-deivce was obvious reduced. > PATCH 1/2: Add blk_plug function for odirect-write block-device > PATCH 2/2: Remove REQ_SYNC for odirect-write in raid456. > > PATCH 2/2 maybe not correct because it alse for odirect-write for regular file. > Jianpeng Ma (2): > fs/block-dev.c:fix performance regression in O_DIRECT writes to > md block devices. In raid5, all requests are submitted by raid5d thread, which already has plug. Why doesn't it work? > raid5: For write performance, remove REQ_SYNC when write was odirect. REQ_SYNC only impacts CFQ, this sounds not reasonable. So the disks are using CFQ ioscheduler. Can you check if you can see the same issue with deadline? Let me guess, without REQ_SYNC, read will get higher priority against write in CFQ, so in this case, write gets delayed, and maybe get better write request merge. And now with REQ_SYNC, read and write has the same priority, there is less request merge. Thanks, Shaohua -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
