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Cygwin: pipe: Fix performance degradation for non-cygwin pipe. 

https://cygwin.com/pipermail/cygwin/2022-December/252628.html

After the commit 9e4d308cd5, 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: 9e4d308cd5 ("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>
This commit is contained in:
Takashi Yano 2022-12-08 22:02:43 +09:00
parent 3a910b624a
commit be635ebc2f
2 changed files with 18 additions and 1 deletions
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16
winsup/cygwin/fhandler/pipe.cc
View File

@ -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)

3
winsup/cygwin/release/3.4.1
View File

@ -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