Jens Axboe wrote:
On Sun, Aug 28 2005, Arjan van de Ven wrote:
On Sun, 2005-08-28 at 05:42 -0400, Jeff Garzik wrote:
The constant ATA_SHT_USE_CLUSTERING in include/linux/libata.h controls
the use of SCSI layer's use_clustering feature, for a great many libata
drivers.
The current setup has clustering disabled, which in theory causes the
block layer to do less work, at the expense of a greater number of
scatter/gather table entries used.
Any opinions WRT turning on clustering for libata?
in 2.4 clustering was expensive due to a large number of checks that
were done (basically the number of fragments got recounted a gazilion
times). In 2.6 Jens fixed that afaik to make it basically free...
at which point it's a win always.
Yeah, it wont cost any extra cycles,
A simple grep for QUEUE_FLAG_CLUSTER-related code shows that it -does-
cost extra cycles.
Imo clustering on the driver level should announce driver capabilities.
If clustering for some arch/kernel makes it slower, that should be
decided at a midlayer level and not in each driver; eg the midlayer
would chose to ignore the drivers capabilities.
So .. my opinion would be that libata should announce the capability (it
seems the code/hw can do it).
Agree, we should just remove the ability to control clustering, as it
really overlaps with the segment settings anyways.
OK, I guess the consensus is to use clustering :)
We'll see if anything blows up in 2.6.14...
Jeff
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