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ib_srpt: Document impact of interrupt assignment on fairness (merge r4447 from trunk)

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git-svn-id: http://svn.code.sf.net/p/scst/svn/branches/2.2.x@4716 d57e44dd-8a1f-0410-8b47-8ef2f437770f
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Bart Van Assche
2013-01-06 14:53:22 +00:00
parent 91cd5b1efa
commit 0c22c21c63
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@@ -338,6 +338,15 @@ storage devices though (SSDs), DEVICE.threads_num should be set to 1 or 2 in
/etc/scst.conf in order to reach optimal performance for small block sizes
(e.g. 4 KB).
When multiple InfiniBand HCA's are present in a target system the Linux
kernel by default will assign the associated interrupt handlers to CPU 0.
Even irqbalance will often assign the interrupt handlers of multiple HCA's
to the same CPU. That is unfortunate because it leads to unfair handling of
SRP sessions. The solution is to assign InfiniBand HCA interrupts manually
to different CPU's. That's possible by writing looking up the InfiniBand
interrupt numbers in /proc/interrupts and by writing proper bitmasks into
/proc/irq/<n>/smp_affinity.
Performance Notes - Initiator Side
----------------------------------