Re: [PATCH] libata-sff: fix 32-bit PIO regression
From: Jeff Garzik
Date: Sun Feb 08 2009 - 19:20:57 EST
Sergei Shtylyov wrote:
Do you really think that the transfers having lengths non-divisible by
4 make any *significant* percentage even on the ATAPI devices? I think
it's you who is really wrong.
The answer depends on workload. Though rare, workloads do exist that
involve a lot of oddball querying via weird, vendor-specific SCSI[-ish]
commands.
Moreover, the likelihood and cost of a branch mispredict are both low in
this case, IMO.
Or a more human version of the rule: if you have to have a long email
thread about unlikely() placement, it is best just to avoid using
unlikely() in that case at all. Branch prediction units in modern CPUs
are damned good anyways, and there is always the likelihood that a
human-placed unlikely() becomes wrong in the future.
Plus the code is more readable without unlikely(), IMO.
Jeff
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