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When mutiple threads waiting for lock at the same time, once lock owner
releases the lock, waiters will see lock available and all try to lock,
which may cause an expensive CAS storm.
Binary exponential backoff with random jitter is introduced. As try-lock
attempt increases, there is more likely that a larger number threads
compete for adaptive mutex lock, so increase wait time in exponential.
A random jitter is also added to avoid synchronous try-lock from other
threads.
v2: Remove read-check before try-lock for performance.
v3:
1. Restore read-check since it works well in some platform.
2. Make backoff arch dependent, and enable it for x86_64.
3. Limit max backoff to reduce latency in large critical section.
v4: Fix strict-prototypes error in sysdeps/nptl/pthread_mutex_backoff.h
v5: Commit log updated for regression in large critical section.
Result of pthread-mutex-locks bench
Test Platform: Xeon 8280L (2 socket, 112 CPUs in total)
First Row: thread number
First Col: critical section length
Values: backoff vs upstream, time based, low is better
non-critical-length: 1
1 2 4 8 16 32 64 112 140
0 0.99 0.58 0.52 0.49 0.43 0.44 0.46 0.52 0.54
1 0.98 0.43 0.56 0.50 0.44 0.45 0.50 0.56 0.57
2 0.99 0.41 0.57 0.51 0.45 0.47 0.48 0.60 0.61
4 0.99 0.45 0.59 0.53 0.48 0.49 0.52 0.64 0.65
8 1.00 0.66 0.71 0.63 0.56 0.59 0.66 0.72 0.71
16 0.97 0.78 0.91 0.73 0.67 0.70 0.79 0.80 0.80
32 0.95 1.17 0.98 0.87 0.82 0.86 0.89 0.90 0.90
64 0.96 0.95 1.01 1.01 0.98 1.00 1.03 0.99 0.99
128 0.99 1.01 1.01 1.17 1.08 1.12 1.02 0.97 1.02
non-critical-length: 32
1 2 4 8 16 32 64 112 140
0 1.03 0.97 0.75 0.65 0.58 0.58 0.56 0.70 0.70
1 0.94 0.95 0.76 0.65 0.58 0.58 0.61 0.71 0.72
2 0.97 0.96 0.77 0.66 0.58 0.59 0.62 0.74 0.74
4 0.99 0.96 0.78 0.66 0.60 0.61 0.66 0.76 0.77
8 0.99 0.99 0.84 0.70 0.64 0.66 0.71 0.80 0.80
16 0.98 0.97 0.95 0.76 0.70 0.73 0.81 0.85 0.84
32 1.04 1.12 1.04 0.89 0.82 0.86 0.93 0.91 0.91
64 0.99 1.15 1.07 1.00 0.99 1.01 1.05 0.99 0.99
128 1.00 1.21 1.20 1.22 1.25 1.31 1.12 1.10 0.99
non-critical-length: 128
1 2 4 8 16 32 64 112 140
0 1.02 1.00 0.99 0.67 0.61 0.61 0.61 0.74 0.73
1 0.95 0.99 1.00 0.68 0.61 0.60 0.60 0.74 0.74
2 1.00 1.04 1.00 0.68 0.59 0.61 0.65 0.76 0.76
4 1.00 0.96 0.98 0.70 0.63 0.63 0.67 0.78 0.77
8 1.01 1.02 0.89 0.73 0.65 0.67 0.71 0.81 0.80
16 0.99 0.96 0.96 0.79 0.71 0.73 0.80 0.84 0.84
32 0.99 0.95 1.05 0.89 0.84 0.85 0.94 0.92 0.91
64 1.00 0.99 1.16 1.04 1.00 1.02 1.06 0.99 0.99
128 1.00 1.06 0.98 1.14 1.39 1.26 1.08 1.02 0.98
There is regression in large critical section. But adaptive mutex is
aimed for "quick" locks. Small critical section is more common when
users choose to use adaptive pthread_mutex.
Signed-off-by: Wangyang Guo <wangyang.guo@intel.com>
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
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Some Linux interfaces never restart after being interrupted by a signal
handler, regardless of the use of SA_RESTART [1]. It means that for
pthread cancellation, if the target thread disables cancellation with
pthread_setcancelstate and calls such interfaces (like poll or select),
it should not see spurious EINTR failures due the internal SIGCANCEL.
However recent changes made pthread_cancel to always sent the internal
signal, regardless of the target thread cancellation status or type.
To fix it, the previous semantic is restored, where the cancel signal
is only sent if the target thread has cancelation enabled in
asynchronous mode.
The cancel state and cancel type is moved back to cancelhandling
and atomic operation are used to synchronize between threads. The
patch essentially revert the following commits:
8c1c0aae20 nptl: Move cancel type out of cancelhandling
2b51742531 nptl: Move cancel state out of cancelhandling
26cfbb7162 nptl: Remove CANCELING_BITMASK
However I changed the atomic operation to follow the internal C11
semantic and removed the MACRO usage, it simplifies a bit the
resulting code (and removes another usage of the old atomic macros).
Checked on x86_64-linux-gnu, i686-linux-gnu, aarch64-linux-gnu,
and powerpc64-linux-gnu.
[1] https://man7.org/linux/man-pages/man7/signal.7.html
Reviewed-by: Florian Weimer <fweimer@redhat.com>
Tested-by: Aurelien Jarno <aurelien@aurel32.net>
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I used these shell commands:
../glibc/scripts/update-copyrights $PWD/../gnulib/build-aux/update-copyright
(cd ../glibc && git commit -am"[this commit message]")
and then ignored the output, which consisted lines saying "FOO: warning:
copyright statement not found" for each of 7061 files FOO.
I then removed trailing white space from math/tgmath.h,
support/tst-support-open-dev-null-range.c, and
sysdeps/x86_64/multiarch/strlen-vec.S, to work around the following
obscure pre-commit check failure diagnostics from Savannah. I don't
know why I run into these diagnostics whereas others evidently do not.
remote: *** 912-#endif
remote: *** 913:
remote: *** 914-
remote: *** error: lines with trailing whitespace found
...
remote: *** error: sysdeps/unix/sysv/linux/statx_cp.c: trailing lines
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We stopped adding "Contributed by" or similar lines in sources in 2012
in favour of git logs and keeping the Contributors section of the
glibc manual up to date. Removing these lines makes the license
header a bit more consistent across files and also removes the
possibility of error in attribution when license blocks or files are
copied across since the contributed-by lines don't actually reflect
reality in those cases.
Move all "Contributed by" and similar lines (Written by, Test by,
etc.) into a new file CONTRIBUTED-BY to retain record of these
contributions. These contributors are also mentioned in
manual/contrib.texi, so we just maintain this additional record as a
courtesy to the earlier developers.
The following scripts were used to filter a list of files to edit in
place and to clean up the CONTRIBUTED-BY file respectively. These
were not added to the glibc sources because they're not expected to be
of any use in future given that this is a one time task:
https://gist.github.com/siddhesh/b5ecac94eabfd72ed2916d6d8157e7dc
https://gist.github.com/siddhesh/15ea1f5e435ace9774f485030695ee02
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
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This commit also moves the aio_misc and aio_sigquue helper,
so GLIBC_PRIVATE exports need to be added.
The symbol was moved using scripts/move-symbol-to-libc.py.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
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This mirrors the situation on Hurd. These directories are on
the include search part, so #include <pthreadP.h> works after this
change on both Hurd and nptl.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
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