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70,000 TLB shootdown IPIs per second
I have been doing some testing on a fileserver recently donated to TNF.
The system has an Areca 1280 controller (arcmsr driver) with a single
RAID6 volume configured on 12 disks; 32GB of RAM; two quad-core Xeon L5420
CPUs.
I have tested under NetBSD-6 and NetBSD-current as well as the tls-maxphys
branch. The test is a 'dd bs=2m of=/test count=65536". Write throughput,
while acceptable (300-350MB/sec; 350-400MB/sec with tls-maxphys) is about
2/3 what I get on the same hardware under Linux. Read throughput is less
good, 250-300MB/sec.
The filesystem is FFSv2, 32k block/4k frag, with WAPBL.
Watching systat while I do the dd tests, I see up to 70,000 TLB shootdown
IPIs per second. Is this really right? I am not sure I know how to count
these under Linux but I don't see any evidence of them. Is there a pmap
problem? I'm running port-amd64.
I have also seen some other odd things I'll detail elsewhere, but just for
a start, can anyone explain to me whether this number of TLB shootdowns
should be expected, whether each should really generate its own IPI, and
what the performance impact may be?
--
Thor Lancelot Simon
tls%panix.com@localhost
It's very complicated. It's very cumbersome. There's a
lot of numbers involved with it.
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