On 5/8/2012 1:28 PM, Roy Sigurd Karlsbakk wrote:
I'm currently spec'ing out a Sandy Bridge Xeon server that would most
likely
run Illumos / SmartOS. This server will initially be running Windows
Server
2008 R2 / Exchange Server and a Debian Linux distribution inside of
KVM.
I'm currently deciding between the Xeon E3-1220 (no Hyper-Threading)
and
E3-1230 (Hyper-Threading). What's the consensus on HT on Illumos/KVM -
could I get a significant performance gain from turning on HT, or is
it
better to leave it off? The VMs are not going to be running any
intensive multithreaded applications.
It might help, but if a system is stressed with or without ht, the one without ht usually
wins, since each "virtual core" with ht will have half the effective cache
size. If memory stress is low, ht may help, though.
Also, I'm planning on getting a SuperMicro X9SCM-F motherboard. It is
my understanding there are no known incompatibilities between this
motherboard and recent releases of Illumos, is that correct?
I only have one X7DB8 and a few X8DTH boards installed with (a recent recent
illumos-based) OpenIndiana, but those work as a dream…
Vennlige hilsener / Best regards
roy
--
Roy hits the biggest nail on the head, here. HT should work just fine
(i.e. give you almost 2x CPU performance) with two major issues:
(1) anything where you're doing a large amount of memory transfers (i.e.
your workload is mostly operating on fresh data, rather than the results
of prior calculations), the lower amount of cache per thread really
hurts, especially if the two threads are huge cache hogs - e.g. doing
large matrix calculations. This ends up cache thrashing, and both
threads suffer horribly.
(2) lots of FP work, since there's still only one FP execution unit
being shared between the two threads.
For ZFS fileserving, I'd be surprised to see either of the two above
cases occur, and thus HT should be beneficial, as ZFS tends to like lots
of threads (and scales well with adding more threading). That said, I
*could* see a place where huge amounts of checksum calculations would be
an issue, but that's about the only case I would anticipate.
Real world experience/metrics would be beneficial here.
Of course, the difference between the -1220 and -1230 is under $25, so
I'd probably chance it with the -1230, as you can shut off HT if it
doesn't work out.
-Erik
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