Date: Mon, 6 Apr 2015 18:40:05 -0700 From: Wim Lewis <wiml@omnigroup.com> To: freebsd-performance@freebsd.org Subject: Capturing a snapshot of user stacks Message-ID: <2B4F43A6-CB6A-4183-8847-968D6EA4CA9A@omnigroup.com>
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I’m looking for a tool which can capture all (or a selected subset) of the user stacks on the system, even for tasks that are blocked in a syscall at the time. Dtrace can capture a user stack but only when an event happens in that task; and procstat -k can capture all the stacks but only the kernel stacks. Is there a way to, in effect, have a dtrace probe fire in every blocked thread? Or another way to get this information? A little explanation: I’m trying to discover why a system occasionally becomes slow. When this happens, I want to capture some profiling information for later perusal. I can get a lot of information from dtrace (a la http://www.brendangregg.com/FlameGraphs/offcpuflamegraphs.html ) and pmc, but that won’t tell me anything about a process that’s blocked the whole time, or is blocked at the start of the interval but unblocks partway through (as is likely to be the case if I only start collecting data once the problem occurs). Any ideas? Wim Lewis / wiml@omnigroup.com
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