Add profiling with signals post #27
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ivoanjo
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Feb 15, 2023
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| > This signal typically indicates the expiration of a timer that measures both CPU time used by the current process, and CPU time expended on behalf of the process by the system. Such a timer is used to implement code profiling facilities, hence the name of this signal. | ||
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| We aren't using many CPU cycles in userspace as we have quickly been de-scheduled. The kernel might be using a bit of CPU for accounting purposes, but in any case it's probably very few CPU cycles, so it would take a very long time to ever a whole 2 seconds of kernel CPU time. |
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In this example I don't think it would ever happen -- the process is sitting on a sleep so the only chance of the signal delivery happening is either before or after the sleep, which unless the CPU is running at 1MHz I don't think would happen :)
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This is a terrible example I agree! I think that the example below with the BPF loading where userspace uses no CPU but the kernel does might be a better thing to bring up. Will reword this :D
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| - [0] [signal-safety(7)](https://man7.org/linux/man-pages/man7/signal-safety.7.html) | ||
| - [1] Go's [`PrintStack`](https://pkg.go.dev/runtime/debug#PrintStack) and Ruby's [`Kernel#Caller`](https://ruby-doc.org/3.2.1/Kernel.html#method-i-caller). | ||
| - Seems like this issue was also found by Daniel. He wrote about it [in his website](https://dxuuu.xyz/bpf-go-pprof.html). |
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The clone system call also seems to potentially suffer from a similar issue, see async-profiler/async-profiler#97 , although there's workarounds for it.
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Signed-off-by: Francisco Javier Honduvilla Coto <[email protected]>
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Signed-off-by: Francisco Javier Honduvilla Coto [email protected]