Re: common signal handler protection

On Tue, Nov 21, 2023 at 03:20:08PM -0600, Nathan Bossart wrote:
> * Overhead: The wrapper handler calls a function pointer and getpid(),
> which AFAICT is a real system call on most platforms. That might not be
> a tremendous amount of overhead, but it's not zero, either. I'm
> particularly worried about signal-heavy code like synchronous
> replication. (Are there other areas that should be tested?) If this is
> a concern, perhaps we could allow certain processes to opt out of this
> wrapper handler, provided we believe it is unlikely to fork or that the
> handler code is safe to run in grandchild processes.

I finally spent some time trying to measure this overhead. Specifically, I
sent many, many SIGUSR2 signals to postmaster, which just uses
dummy_handler(), i.e., does nothing. I was just barely able to get
wrapper_handler() to show up in the first page of 'perf top' in this
extreme case, which leads me to think that the overhead might not be a
problem.

--
Nathan Bossart
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