From: Will Newton <will.newton@linaro.org>
To: Bernie Ogden <bernie.ogden@linaro.org>
Cc: "libc-ports@sourceware.org" <libc-ports@sourceware.org>,
libc-alpha <libc-alpha@sourceware.org>
Subject: Re: [PATCH] Remove arm lowlevellock.c
Date: Mon, 28 Apr 2014 14:56:00 -0000 [thread overview]
Message-ID: <CANu=Dmjz96Nk-C0xWOdO-xDWzt=+Z7u6OrsYJehcB_Y0T7B=ag@mail.gmail.com> (raw)
In-Reply-To: <CALE0ps2nxAqHeotsxVcBEOV+nRsFGLBLD8+kP2ZY-PdnELkueA@mail.gmail.com>
Hi Bernie,
ARM patches can now be sent to libc-alpha as ARM has moved from ports
into the main tree.
I'm not sure if we still use libc-ports for HPPA patches...
On 28 April 2014 15:50, Bernie Ogden <bernie.ogden@linaro.org> wrote:
> lowlevellock.c for arm differs from the generic lowlevellock.c only in
> insignificant ways, so can be removed. Happily, this fixes BZ 15119
> (unnecessary busy loop in __lll_timedlock_wait on arm).
>
> The notable differences between the arm and generic implementations are:
>
> 1) arm __lll_timedlock_wait has a fast path out if futex has been set
> to 0 between since the function was called. This seems unlikely to
> happen very often, so it seems at worst harmless to lose this fast
> path.
>
> 2) Some function in arm's lowlevellock.c set futex to 2 if it was 1.
> The generic version always sets the futex to 2. As futex can only be
> 0, 1 or 2 on entry into these functions, the behaviour is equivalent.
> (If the futex manages to be 0 on entry then we've just lost another
> unlikely fast path out.)
>
> There are no test suite regressions.
>
> Note that hppa and sparc also have their own lowlevellock.c. I believe
> hppa can also be removed, so I'll send a separate patch for that
> shortly. sparc's seems to be genuinely needed as it uses a different
> locking structure.
>
> Also note that the analysis at
> https://sourceware.org/ml/libc-ports/2013-02/msg00021.html indicates a
> further locking performance bug to fix - I've got a partial patch for
> that which I can submit once I've finished testing.
>
> 2014-04-24 Bernard Ogden <bernie.ogden@linaro.org>
>
> [BZ #15119]
> * sysdeps/unix/sysv/linux/arm/nptl/lowlevellock.c: Remove file.
>
>
> diff --git a/sysdeps/unix/sysv/linux/arm/nptl/lowlevellock.c
> b/sysdeps/unix/sysv/linux/arm/nptl/lowlevellock.c
> deleted file mode 100644
> index 9603d7b..0000000
> --- a/sysdeps/unix/sysv/linux/arm/nptl/lowlevellock.c
> +++ /dev/null
> @@ -1,132 +0,0 @@
> -/* low level locking for pthread library. Generic futex-using version.
> - Copyright (C) 2003-2014 Free Software Foundation, Inc.
> - This file is part of the GNU C Library.
> -
> - The GNU C Library is free software; you can redistribute it and/or
> - modify it under the terms of the GNU Lesser General Public
> - License as published by the Free Software Foundation; either
> - version 2.1 of the License, or (at your option) any later version.
> -
> - The GNU C Library is distributed in the hope that it will be useful,
> - but WITHOUT ANY WARRANTY; without even the implied warranty of
> - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> - Lesser General Public License for more details.
> -
> - You should have received a copy of the GNU Lesser General Public
> - License along with the GNU C Library. If not, see
> - <http://www.gnu.org/licenses/>. */
> -
> -#include <errno.h>
> -#include <sysdep.h>
> -#include <lowlevellock.h>
> -#include <sys/time.h>
> -
> -void
> -__lll_lock_wait_private (int *futex)
> -{
> - do
> - {
> - int oldval = atomic_compare_and_exchange_val_acq (futex, 2, 1);
> - if (oldval != 0)
> - lll_futex_wait (futex, 2, LLL_PRIVATE);
> - }
> - while (atomic_compare_and_exchange_bool_acq (futex, 2, 0) != 0);
> -}
> -
> -
> -/* These functions don't get included in libc.so */
> -#ifdef IS_IN_libpthread
> -void
> -__lll_lock_wait (int *futex, int private)
> -{
> - do
> - {
> - int oldval = atomic_compare_and_exchange_val_acq (futex, 2, 1);
> - if (oldval != 0)
> - lll_futex_wait (futex, 2, private);
> - }
> - while (atomic_compare_and_exchange_bool_acq (futex, 2, 0) != 0);
> -}
> -
> -
> -int
> -__lll_timedlock_wait (int *futex, const struct timespec *abstime, int private)
> -{
> - struct timespec rt;
> -
> - /* Reject invalid timeouts. */
> - if (abstime->tv_nsec < 0 || abstime->tv_nsec >= 1000000000)
> - return EINVAL;
> -
> - /* Upgrade the lock. */
> - if (atomic_exchange_acq (futex, 2) == 0)
> - return 0;
> -
> - do
> - {
> - struct timeval tv;
> -
> - /* Get the current time. */
> - (void) __gettimeofday (&tv, NULL);
> -
> - /* Compute relative timeout. */
> - rt.tv_sec = abstime->tv_sec - tv.tv_sec;
> - rt.tv_nsec = abstime->tv_nsec - tv.tv_usec * 1000;
> - if (rt.tv_nsec < 0)
> - {
> - rt.tv_nsec += 1000000000;
> - --rt.tv_sec;
> - }
> -
> - /* Already timed out? */
> - if (rt.tv_sec < 0)
> - return ETIMEDOUT;
> -
> - // XYZ: Lost the lock to check whether it was private.
> - lll_futex_timed_wait (futex, 2, &rt, private);
> - }
> - while (atomic_compare_and_exchange_bool_acq (futex, 2, 0) != 0);
> -
> - return 0;
> -}
> -
> -
> -int
> -__lll_timedwait_tid (int *tidp, const struct timespec *abstime)
> -{
> - int tid;
> -
> - if (abstime->tv_nsec < 0 || abstime->tv_nsec >= 1000000000)
> - return EINVAL;
> -
> - /* Repeat until thread terminated. */
> - while ((tid = *tidp) != 0)
> - {
> - struct timeval tv;
> - struct timespec rt;
> -
> - /* Get the current time. */
> - (void) __gettimeofday (&tv, NULL);
> -
> - /* Compute relative timeout. */
> - rt.tv_sec = abstime->tv_sec - tv.tv_sec;
> - rt.tv_nsec = abstime->tv_nsec - tv.tv_usec * 1000;
> - if (rt.tv_nsec < 0)
> - {
> - rt.tv_nsec += 1000000000;
> - --rt.tv_sec;
> - }
> -
> - /* Already timed out? */
> - if (rt.tv_sec < 0)
> - return ETIMEDOUT;
> -
> - /* Wait until thread terminates. */
> - // XYZ: Lost the lock to check whether it was private.
> - if (lll_futex_timed_wait (tidp, tid, &rt, LLL_SHARED) == -ETIMEDOUT)
> - return ETIMEDOUT;
> - }
> -
> - return 0;
> -}
> -#endif
--
Will Newton
Toolchain Working Group, Linaro
next prev parent reply other threads:[~2014-04-28 14:56 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-28 14:50 Bernie Ogden
2014-04-28 14:56 ` Will Newton [this message]
2014-04-29 15:26 ` Joseph S. Myers
2014-04-30 12:58 ` Bernie Ogden
2014-04-30 15:50 ` Joseph S. Myers
2014-05-01 13:03 ` Bernie Ogden
2014-05-01 13:29 ` Will Newton
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CANu=Dmjz96Nk-C0xWOdO-xDWzt=+Z7u6OrsYJehcB_Y0T7B=ag@mail.gmail.com' \
--to=will.newton@linaro.org \
--cc=bernie.ogden@linaro.org \
--cc=libc-alpha@sourceware.org \
--cc=libc-ports@sourceware.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).