From: Sultan Alsawaf <sultan@kerneltoast.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>,
Thomas Hellstrom <thellstrom@vmware.com>,
Palmer Dabbelt <palmer@sifive.com>,
Sakari Ailus <sakari.ailus@linux.intel.com>,
Ming Lei <ming.lei@redhat.com>,
Gal Pressman <galpress@amazon.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] scatterlist: Speed up for_each_sg() loop macro
Date: Mon, 28 Oct 2019 09:18:48 -0700 [thread overview]
Message-ID: <20191028161848.GA32593@sultan-box.localdomain> (raw)
In-Reply-To: <20191028141734.GD29652@ziepe.ca>
On Mon, Oct 28, 2019 at 11:17:34AM -0300, Jason Gunthorpe wrote:
> This is a big change in the algorithm, why are you sure it is OK?
I'm sure it's OK because the test module I provided in the commit message
encapsulates all the possible edge cases of sg chaining:
-An sglist with >=1 && <=(SG_MAX_SINGLE_ALLOC-1) nents (no chaining, the last
element in the array is unused)
-An sglist with SG_MAX_SINGLE_ALLOC nents (no chaining, the last element in the
array isn't an sg chain link)
-An sglist with >SG_MAX_SINGLE_ALLOC && <=2*(SG_MAX_SINGLE_ALLOC-1) nents (there
is one chain to another array, and the other array's last element is unused)
-An sglist with (2*SG_MAX_SINGLE_ALLOC)-1 nents (there is one chain to another
array, and the other array's last element isn't an sg chain link)
-An sglist with 2*SG_MAX_SINGLE_ALLOC nents (there are two chains to other
arrays, and the 3rd array contains 2 sgs & its last element is unused)
-An sglist with >2*SG_MAX_SINGLE_ALLOC && <(3*SG_MAX_SINGLE_ALLOC)-1 nents
(there are two chains to other arrays, and the 3rd array's last element isn't
an sg chain)
I just made my module test nents >=1 && <=3*SG_MAX_SINGLE_ALLOC for simplicity.
My proposed for_each_sg() also handles nents==0 the same as before by doing
nothing.
> Did you compare with just inlining sg_net?
Yes. Forcefully inlining sg_next() had no impact on performance.
Sultan
next prev parent reply other threads:[~2019-10-28 16:18 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-25 21:33 [PATCH] scatterlist: Speed up for_each_sg() loop macro Sultan Alsawaf
2019-10-28 14:17 ` Jason Gunthorpe
2019-10-28 16:18 ` Sultan Alsawaf [this message]
2019-10-28 16:23 ` Jason Gunthorpe
2019-10-28 16:28 ` Christoph Hellwig
2019-10-28 16:37 ` Sultan Alsawaf
2019-10-28 16:29 ` Sultan Alsawaf
2019-10-28 23:46 ` kbuild test robot
2019-10-29 2:25 ` Ming Lei
2019-11-01 3:33 ` [scatterlist] 8f39742f03: suspend_stress.fail kernel test robot
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