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feedback from google
- From: "Chen, Brad" <brad dot chen at intel dot com>
- To: <systemtap at sources dot redhat dot com>
- Date: Fri, 13 May 2005 09:53:21 -0700
- Subject: feedback from google
Earlier we were looking for stronger justification for
scrutinizing kprobes performance; why "high-frequency"
probes executing over 5KHz would matter to anybody. I
was talking with a friend at Google today (Dick Sites)
about Systemtap and he jumped on this immediately as
an issue. He suggested a couple examples off the top
of his head of things we'd want to monitor that pushed
well above the 1KHz event frequency range:
- context switches. Just moving the mouse around on
the desktop can generate context switches at over 2KHz.
Peak context switch rates are probably over 100K events
per second; are we ready?
- network interrupts. A Gb Ethernet receiving full-sized
packets at full rates would generate about 80K network
interrupts per second. Smaller packets could be worse.
Actually, if you just do the arithmetic of peak rates
for things like page faults, disk requests, system calls
etc. it's easy to find cases that involve interrupt
rates much higher than 5KHz.
Sites was happy to hear about the Systemtap effort and
sounds like he would eager to give it a try. One tool he
suggested was to generate a trace of lock, disk, network
and inter-processor notification events, basically
everything that could possibly be related to unwanted
idle time on a performance critical system. Probably not
realistic for our first system but might be a good test
case with a faster version of kprobes.
For the record, I have no expectation that kprobes
performance work can happen in time for the first release.
Brad