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SubjectRe: [PATCH] block: fix q->max_segment_size checking in blk_recalc_rq_segments about VMERGE
On Thu, 24 Jul 2008, James Bottomley wrote:

> On Thu, 2008-07-24 at 11:07 -0400, Mikulas Patocka wrote:
> > So try to #define BIO_VMERGE_BOUNDARY 0 for Pa-Risc and tell us what
> > performance degradation do you see (and what driver do you use and what is
> > the I/O pattern).
> >
> > If you show something specific, we can consider that --- but you haven't
> > yet told us anything, except generic talk.
>
> You keep ignoring inconvenient facts. For about the third time:
>
> I run a test bed for sg_tables (large chaining of requests). This runs
> on parisc using virtual merging (has to because the final physical table
> size can't go over the sg list of the SCSI card). If I turn off virtual
> merging I can no longer test sg_tables in vanilla kernels.
>
> James

What sg_tables test do you mean? What does the test do? Why couldn't you
run the test if BIO_VMERGE_BOUNDARY is 0? Normal I/O obviously can work
with BIO_VMERGE_BOUNDARY 0, the kernel will just send more smaller
requests.

Mikulas


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