https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=be635ebc2f5df7f07ebc3f1f9531f38e3c09c970
commit be635ebc2f5df7f07ebc3f1f9531f38e3c09c970 Author: Takashi Yano <[email protected]> Date: Thu Dec 8 22:02:43 2022 +0900 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 <[email protected]> Reviewed-by: Corinna Vinschen <[email protected]> Signed-off-by: Takashi Yano <[email protected]> Diff: --- winsup/cygwin/fhandler/pipe.cc | 16 +++++++++++++++- winsup/cygwin/release/3.4.1 | 3 +++ 2 files changed, 18 insertions(+), 1 deletion(-) 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) diff --git a/winsup/cygwin/release/3.4.1 b/winsup/cygwin/release/3.4.1 index 226329d9c..9a831eda5 100644 --- a/winsup/cygwin/release/3.4.1 +++ b/winsup/cygwin/release/3.4.1 @@ -10,3 +10,6 @@ Bug Fixes compiled under Cygwin 3.4.0 having a public facing interface using FILE need to be recompiled. Addresses: https://savannah.gnu.org/bugs/index.php?63480 + +- Fix performance degradation of non-cygwin pipe. + Addresses: https://cygwin.com/pipermail/cygwin/2022-December/252628.html
