diff options
| author | Takashi Yano <takashi.yano@nifty.ne.jp> | 2022-12-08 16:02:43 +0300 |
|---|---|---|
| committer | Takashi Yano <takashi.yano@nifty.ne.jp> | 2022-12-09 15:01:29 +0300 |
| commit | be635ebc2f5df7f07ebc3f1f9531f38e3c09c970 (patch) | |
| tree | 6961508f11782620c3a393faa6b5039b4f0af0c5 /winsup/cygwin/fhandler | |
| parent | 3a910b624a1bcd3d2ee625a308ba9f108a152fb7 (diff) | |
Cygwin: pipe: Fix performance degradation for non-cygwin pipe.
https://cygwin.com/pipermail/cygwin/2022-December/252628.html
After the commit 9e4d308cd592, the performance of read from non-cygwin
pipe has been degraded. This is because select_sem mechanism does not
work for non-cygwin pipe. This patch fixes the issue.
Fixes: 9e4d308cd592 ("Cygwin: pipe: Adopt FILE_SYNCHRONOUS_IO_NONALERT
flag for read pipe.")
Reported-by: tryandbuy <tryandbuy@proton.me>
Reviewed-by: Corinna Vinschen <corinna@vinschen.de>
Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>
Diffstat (limited to 'winsup/cygwin/fhandler')
| -rw-r--r-- | winsup/cygwin/fhandler/pipe.cc | 16 |
1 files changed, 15 insertions, 1 deletions
diff --git a/winsup/cygwin/fhandler/pipe.cc b/winsup/cygwin/fhandler/pipe.cc index 94b85c349..e72ee65ca 100644 --- a/winsup/cygwin/fhandler/pipe.cc +++ b/winsup/cygwin/fhandler/pipe.cc @@ -281,6 +281,8 @@ fhandler_pipe::raw_read (void *ptr, size_t& len) size_t nbytes = 0; NTSTATUS status = STATUS_SUCCESS; IO_STATUS_BLOCK io; + ULONGLONG t0 = GetTickCount64 (); /* Init timer */ + const ULONGLONG t0_threshold = 20; if (!len) return; @@ -312,6 +314,7 @@ fhandler_pipe::raw_read (void *ptr, size_t& len) { ULONG_PTR nbytes_now = 0; ULONG len1 = (ULONG) (len - nbytes); + DWORD select_sem_timeout = 0; FILE_PIPE_LOCAL_INFORMATION fpli; status = NtQueryInformationFile (get_handle (), &io, @@ -358,7 +361,18 @@ fhandler_pipe::raw_read (void *ptr, size_t& len) nbytes = (size_t) -1; break; } - waitret = cygwait (select_sem, 1); + /* If the pipe is a non-cygwin pipe, select_sem trick + does not work. As a result, the following cygwait() + will return only after timeout occurs. This causes + performance degradation. However, setting timeout + to zero causes high CPU load. So, set timeout to + non-zero only when select_sem is valid or pipe is + not ready to read for more than t0_threshold. + This prevents both the performance degradation and + the high CPU load. */ + if (select_sem || GetTickCount64 () - t0 > t0_threshold) + select_sem_timeout = 1; + waitret = cygwait (select_sem, select_sem_timeout); if (waitret == WAIT_CANCELED) pthread::static_cancel_self (); else if (waitret == WAIT_SIGNALED) |