Messages in this thread | | | Date | Mon, 21 Feb 2005 16:41:51 -0800 | From | Pete Zaitcev <> | Subject | Re: Merging fails reading /dev/uba1 |
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On Mon, 21 Feb 2005 12:00:48 -0800 (PST), Linus Torvalds <torvalds@osdl.org> wrote:
> That said, I'm surprised that the difference in performance is _that_ > large. Regardless of whether the disk blocksize is 512 bytes or 4096 > bytes, you should be getting IO merging - it might use more CPU time, but > the actual IO should still be done in much larger blocks.
I am surprised too. Jens says "ub effectively disables merging by setting max hw/phys segment limit of 1." But surely this ought not to be a problem for reads within the same page.
> int size = 4096; > ioctl(fd, BLKBSZSET, &size);
Thank you for the tip. This works fine, 4KB I/O is restored for dd. However, I still have this problem with people who use ub to read CF sticks from their cameras, mounted as FAT or VFAT. I verified that the effect of this ioctl disappears at mount time, just as you said.
I'll think what I can do about it.
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