On 08/12/10 04:16, Steve Gonczi wrote:
Greetings,
I am seeing some unexplained performance drop using the above cpus,
using a fairly up-to-date build ( late 145).
Basically, the system seems to be 98% idle, spending most if its time in this
stack:
unix`i86_mwait+0xd
unix`cpu_idle_mwait+0xf1
unix`idle+0x114
unix`thread_start+0x8
455645
Most cpus seem to be idling most of the time, sitting on the mwait instruction.
No lock contention, not waiting on io, I am finding myself at a loss explaining
what this system is doing.
(I am monitoring the system w. lockstat, mpstat, prstat). Despite the
predominantly idle system,
I see some latency reported by prstat microstate accounting on the zfs threads.
This is a fairly beefy box, 24G memory, 16 cpus.
Doing a local zfs send | receive, should be getting at least 100MB+,
and I am only getting 5-10MB.
I see some Intel errata on the 55xx series xeons, a problem with the
monitor/mwait instructions, that could conceivably cause missed wake-up or
mis-reported mwait status.
I'd suggest you supply a bit more information (to the list, not to me, I
don't know very much about zfs internals):
- zpool/zfs configuration
- history of this issue: has it been like this since you installed the
machine?
- if no: what changes were introduced around the time you saw this first?
- does this happen on a busy machine too?
- describe your test in more detail
- provide measurements (lockstat, iostat, maybe some DTrace) before and
during test, add some timestamps so people can correlate data to events.
- anything else you can think of that might be relevant.
HTH
Michael
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