Hello, I wrote:
The answer depends on workload. Though rare, workloads do exist that
involve a lot of oddball querying via weird, vendor-specific
SCSI[-ish] commands.
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.
Can you give an example of a *continous* querying with the data
transferring commands?
Hm, it just occured to me that the typical ATAPI command packet is
12 bytes long.
Haha, I even can't count! 12 divides by 4, of course. :-D
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. Moreover, the likelihood and cost of a branch mispredict are
both low in this case, IMO.
There are still CPUs without the branch prediction, you know --
Linux runs not only on x86.
Plus the code is more readable without unlikely(), IMO.
I tend to disagree. However, the packet command transfer is not
unlikely at all, so I'll remove that unlikely() in the respun patch.
No, I'll keep it now. This case is indeed unlikely.
Jeff
MBR, Sergei
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