From: Jens Axboe <[EMAIL PROTECTED]>
Subject: Re: [PATCH v2] add bidi support for block pc requests
Date: Wed, 16 May 2007 19:53:22 +0200
> On Wed, May 16 2007, Boaz Harrosh wrote:
> > Boaz Harrosh wrote:
> > > James Bottomley wrote:
> > >>
> > >> There's actually a fourth option you haven't considered:
> > >>
> > >> Roll all the required sglist definitions (request_bufflen,
> > >> request_buffer, use_sg and sglist_len) into the sgtable pools.
> > >>
> > > This is a grate Idea. Let me see if I understand what you mean.
> > > ...
> > > ...
> >
> > Hi Dear James, list.
> > I have worked on proposed solution (If anyone is interested see
> > url blow)
> >
> > Now it works and all but I hit some problems.
> > What happens is that in 64 bit architectures, well in x86_64,
> > the sizeof scatterlist structure is 32 bytes which means that
> > we can only fit exactly 128 of them in a page. But together with
> > the scsi_sg_table header we are down to 127. Also if we want
> > good alignment/packing of other sized pools we want:
> > static struct scsi_host_sg_pool scsi_sg_pools[] = {
> > SP(7),
> > SP(15),
> > SP(31),
> > SP(63),
> > SP(127)
> > };
> >
> > now there are 2 issues with this:
> > 1. Even if I do blk_queue_max_phys_segments(q, 127); I still get
> > requests for use_sg=128 which will crash the kernel.
>
> That sounds like a serious issue, it should definitely not happen. Stuff
> like that would bite other drivers as well, are you absolutely sure that
> is happening? Power-of-2 bug in your code, or in the SCSI code?
Boaz, how do you send requests to the scsi-ml, via fs, sg, or bsg?
> > If anyone wants to see I have done 2 versions of this work. One on top
> > of Jens's sg-chaining work (ver 5). And one on top of Tomo's cleanup
> > git. both can be found here:
> > http://www.bhalevy.com/open-osd/download/scsi_sg_table/
>
> +#define scsi_for_each_sg(cmd, sg, nseg, __i) \
> + for (__i = 0, sg = scsi_sglist(cmd); __i < (nseg); __i++, (sg)++)
>
> Hmm?
When for_each_sg is ready, we convert scsi_for_each_sg to use
for_each_sg. I finished the cleanups on more than 40 drivers on the
top of your patches.
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