On Mon, May 30 2016, Joey Liao wrote: > Hi, > > I have no idea why does raid0_run() in raid0.c use > blk_queue_max_hw_sectors() to set max_hw_sectors as the chunk size, > but the other raid types doesn't? git is your friend.... admittedly you need the 'history' git tree to go back before 2.6.12, but it is available. http://git.kernel.org/cgit/linux/kernel/git/history/history.git/commit/?id=f556ef000efc90a45a285f4f0b4fd70bb70f > > What's the purpose to limit the max_hw_sectors in raid0? unfortunately the commit doesn't answer that question. I think it was to ensure requests larger than one chunk were not created. If they were they would just have to be split, so there is no much to gain. > > Is it related to the source code logic issue or the performance issue? > > Besides, I have an interesting observation. If I remove all the > following queue limitation codes in raid0_run() of raid0.c, the block > size in iostat is still the same as chunk size even the input block > size is much larger than the chunk size. Why??? Because when you write to a RAID0 you *must* divide each request up into chunk-sizes sub-requests, and send them to different devices. NeilBrown > > - blk_queue_max_hw_sectors(mddev->queue, mddev->chunk_sectors); > - blk_queue_max_write_same_sectors(mddev->queue, mddev->chunk_sectors); > + //blk_queue_max_hw_sectors(mddev->queue, mddev->chunk_sectors); > + //blk_queue_max_write_same_sectors(mddev->queue, mddev->chunk_sectors); > > - blk_queue_io_min(mddev->queue, mddev->chunk_sectors << 9); > - blk_queue_io_opt(mddev->queue, > - (mddev->chunk_sectors << 9) * mddev->raid_disks); > + //blk_queue_io_min(mddev->queue, mddev->chunk_sectors << 9); > + /*blk_queue_io_opt(mddev->queue, > + (mddev->chunk_sectors << 9) * mddev->raid_disks);*/ > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html
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