How fast are Linux pipes anyway?

Re:How fast are Linux pipes anyway? by nequo on Thursday June 02, 2022 @12:19PM (#31596817)

Wow, this does 160 MiB/s. That's a huge improvement! The output of strace looks completely different:

  poll([{fd=1, events=POLLOUT}], 1, 0)    = 1 ([{fd=1, revents=POLLOUT}])
  write(1, "11111111111111111111111111111111"..., 8192) = 8192
  poll([{fd=1, events=POLLOUT}], 1, 0)    = 1 ([{fd=1, revents=POLLOUT}])
  write(1, "11111111111111111111111111111111"..., 8192) = 8192

With the recursive code, it buffered the output in the same way but bugged the kernel a whole lot more in-between writes. Not exactly sure what is going on:

  poll([{fd=1, events=POLLOUT}], 1, 0)    = 1 ([{fd=1, revents=POLLOUT}])
  write(1, "11111111111111111111111111111111"..., 8192) = 8192
  rt_sigprocmask(SIG_BLOCK, [INT], [], 8) = 0
  clock_gettime(CLOCK_PROCESS_CPUTIME_ID, {tv_sec=0, tv_nsec=920390843}) = 0
  rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
  rt_sigprocmask(SIG_BLOCK, [INT], [], 8) = 0
  clock_gettime(CLOCK_PROCESS_CPUTIME_ID, {tv_sec=0, tv_nsec=920666397}) = 0
  ...
  rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
  poll([{fd=1, events=POLLOUT}], 1, 0)    = 1 ([{fd=1, revents=POLLOUT}])
  write(1, "11111111111111111111111111111111"..., 8192) = 8192

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Re:How fast are Linux pipes anyway? by dllthomas on Thursday June 02, 2022 @12:28PM (#31596953)

I'm honestly surprised either of them wind up buffered! That must be a change since I stopped paying as much attention to GHC.

I'm also not sure what's going on in the second case. IIRC, at some point historically, a sufficiently tight loop could cause trouble with handling SIGINT, so it might be related to some overagressive workaround for that?

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