Messages in this thread | | | Date | Tue, 26 May 2009 14:23:38 +0900 | Subject | Re: [PATCH 03/13] scsi: unify allocation of scsi command and sense buffer | From | FUJITA Tomonori <> |
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On Mon, 25 May 2009 12:28:01 +0300 Boaz Harrosh <bharrosh@panasas.com> wrote:
> On 05/25/2009 10:30 AM, Jens Axboe wrote: > > Fold the sense buffer into the command, thereby eliminating a slab > > allocation and free per command. > > > > Signed-off-by: Jens Axboe <jens.axboe@oracle.com> > > Jens Hi. > > I'm "TO:" this to Tomo. > > This is the way it used to be for a long time. It was only recently changed by > Tomo because of a bug on none-cache-coherent arches that need to dma-access the > sense_buffer and also on the other hand change scsi_cmnd members by CPU. > > In my opinion all you need is an __aligned(SMP_CACHE_BYTES) declaration at > sense_buffer[] and let there be a hole at the end before the array. But Tomo > did not like that, so he separated the two.
IIRC, it was not my opinion :) I don't think that putting CACHE_ALIGNMENT here is a good idea though.
If this separated sense buffer allocation actually hurts the performance, then I prefer the ->alloc_cmnd and ->destroy_cmnd hook idea. Then most of llds are happy about the current sense buffer scheme and some can use ->alloc_cmnd and ->destroy_cmnd hooks for the better performance.
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