Messages in this thread | | | From | Badari Pulavarty <> | Subject | Re: [PATCH] O_DIRECT with hardware blocksize alignment | Date | Tue, 15 Jan 2002 13:23:06 -0800 (PST) |
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Wouldn't this cause, single IO to split into (possibly) 3 I/Os for RAW VARY on all unaligned IOs ? In that case, wouldn't it be better of doing entire I/O with 512byte buffer heads, so that all of them can be merged ?
IMHO, preventing the merge due to b_size mismatch just to handle few drivers/hardware may be overkill. This will penalize all the drivers which can handle variable size IOs also. Isn't it ? Leaving it to the driver and doing variable size I/O on only the drivers that can handle them, may be a better option ?
In my initial version of RAW VARY patch, I split the I/Os into possibly 3 I/O in raw.c. Do brw_kiovec(.., 512) for the first page and last pages & 4K for the middle pages. It showed reduction in CPU utilization for large IOs. But it since it could split single I/O into 3 I/Os, i did not see significant I/O throughput improvement.
Regards, Badari
> > On Tue, Jan 15 2002, Jens Axboe wrote: > > On Tue, Jan 15 2002, Andrea Arcangeli wrote: > > > actually we could also forbid merging at the ll_rw_block layer if b_size > > > is not equal, maybe that's the simpler solution to that problem after > > > all, merging between kiovec I/O and buffered I/O probably doesn't > > > matter. > > > > Agreed, this is also what I suggested. > > Here's the right version, sorry. This still potentially decrements > elevator sequence wrongly for a missed front merge, but that's an issue > I can definitely live with :-) > .... - 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/
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