Re: [PATCH] scsi: Remove some false sharing in Scsi_Host / Scsi_Device

[Christoph Hellwig]

On Fri, Jul 11, 2014 at 01:25:10PM -0700, Andi Kleen wrote:
> From: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> 
> These data structures are accessed by different CPUs and have some
> fields which are mostly read only and others which are frequently
> written. Separate some common ones into separate cache line
> to minimize false sharing while submitting a command.
> 
> This allows scsi_dispatch_cmd to do more work with shared clean
> cache lines.
> 
> - Move the cmd_serial_number to the end before the host data
> - Separate write common fields from read mostly fields in
> the scsi device

Looks useful, but please provide some numbers on how this actually
helps.

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