From: Eric Blake <eblake@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org
Cc: stefanha@redhat.com
Subject: Re: [Qemu-devel] [PATCH 09/16] qemu-thread: introduce QemuLockCnt
Date: Mon, 8 Feb 2016 15:38:42 -0700 [thread overview]
Message-ID: <56B918F2.9020107@redhat.com> (raw)
In-Reply-To: <1454948107-11844-10-git-send-email-pbonzini@redhat.com>
[-- Attachment #1: Type: text/plain, Size: 2191 bytes --]
On 02/08/2016 09:15 AM, Paolo Bonzini wrote:
> A QemuLockCnt comprises a counter and a mutex, with primitives
> to increment and decrement the counter, and to take and release the
> mutex. It can be used to do lock-free visits to a data structure
> whenever mutexes would be too heavy-weight and the critical section
> is too long for RCU.
>
> This could be implemented simply by protecting the counter with the
> mutex, but QemuLockCnt is harder to misuse and more efficient.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> docs/lockcnt.txt | 343 ++++++++++++++++++++++++++++++++++++++++++++++++++
> include/qemu/thread.h | 17 +++
> util/Makefile.objs | 1 +
> util/lockcnt.c | 122 ++++++++++++++++++
> 4 files changed, 483 insertions(+)
> create mode 100644 docs/lockcnt.txt
> create mode 100644 util/lockcnt.c
>
> diff --git a/docs/lockcnt.txt b/docs/lockcnt.txt
> new file mode 100644
> index 0000000..fc5d240
> --- /dev/null
> +++ b/docs/lockcnt.txt
> @@ -0,0 +1,343 @@
> +DOCUMENTATION FOR LOCKED COUNTERS (aka QemuLockCnt)
> +===================================================
Worth an explicit mention that this document is GPLv2+ (or an explicit
choice of a different license)?
> +
> +QEMU often uses reference counts to track data structures that are being
> +accessed and should not be freed. For example, a loop that invoke
s/invoke/invokes/
> +callbacks like this is not safe:
> +
but overall a nice writeup.
I'll leave the code review to others, though.
> +++ b/util/lockcnt.c
> @@ -0,0 +1,122 @@
> +/*
> + * QemuLockCnt implementation
> + *
> + * Copyright Red Hat, Inc. 2015
> + *
> + * Author:
> + * Paolo Bonzini <pbonzini@redhat.com>
> + */
> +#include <stdlib.h>
> +#include <stdio.h>
> +#include <errno.h>
> +#include <time.h>
> +#include <signal.h>
> +#include <stdint.h>
> +#include <string.h>
> +#include <limits.h>
> +#include <unistd.h>
> +#include <sys/time.h>
You'll want to use qemu/osdep.h in place of several of these headers.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 604 bytes --]
next prev parent reply other threads:[~2016-02-08 22:38 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-08 16:14 [Qemu-devel] [PATCH v2 00/16] aio: first part of aio_context_acquire/release pushdown Paolo Bonzini
2016-02-08 16:14 ` [Qemu-devel] [PATCH 01/16] aio: introduce aio_context_in_iothread Paolo Bonzini
2016-02-08 16:14 ` [Qemu-devel] [PATCH 02/16] aio: do not really acquire/release the main AIO context Paolo Bonzini
2016-02-08 16:14 ` [Qemu-devel] [PATCH 03/16] aio: introduce aio_poll_internal Paolo Bonzini
2016-02-08 16:14 ` [Qemu-devel] [PATCH 04/16] aio: only call aio_poll_internal from iothread Paolo Bonzini
2016-02-08 22:22 ` Eric Blake
2016-02-08 16:14 ` [Qemu-devel] [PATCH 05/16] iothread: release AioContext around aio_poll Paolo Bonzini
2016-02-08 16:14 ` [Qemu-devel] [PATCH 06/16] qemu-thread: introduce QemuRecMutex Paolo Bonzini
2016-02-08 16:14 ` [Qemu-devel] [PATCH 07/16] aio: convert from RFifoLock to QemuRecMutex Paolo Bonzini
2016-02-08 16:14 ` [Qemu-devel] [PATCH 08/16] aio: rename bh_lock to list_lock Paolo Bonzini
2016-02-08 16:15 ` [Qemu-devel] [PATCH 09/16] qemu-thread: introduce QemuLockCnt Paolo Bonzini
2016-02-08 22:38 ` Eric Blake [this message]
2016-02-08 16:15 ` [Qemu-devel] [PATCH 10/16] aio: make ctx->list_lock a QemuLockCnt, subsuming ctx->walking_bh Paolo Bonzini
2016-02-08 16:15 ` [Qemu-devel] [PATCH 11/16] qemu-thread: optimize QemuLockCnt with futexes on Linux Paolo Bonzini
2016-02-08 16:15 ` [Qemu-devel] [PATCH 12/16] aio: tweak walking in dispatch phase Paolo Bonzini
2016-02-08 16:15 ` [Qemu-devel] [PATCH 13/16] aio-posix: remove walking_handlers, protecting AioHandler list with list_lock Paolo Bonzini
2016-02-08 16:15 ` [Qemu-devel] [PATCH 14/16] aio-win32: " Paolo Bonzini
2016-02-08 16:15 ` [Qemu-devel] [PATCH 15/16] aio: document locking Paolo Bonzini
2016-02-08 16:15 ` [Qemu-devel] [PATCH 16/16] aio: push aio_context_acquire/release down to dispatching Paolo Bonzini
-- strict thread matches above, loose matches on Subject: below --
2016-02-09 11:45 [Qemu-devel] [PATCH v3 00/16] aio: first part of aio_context_acquire/release pushdown Paolo Bonzini
2016-02-09 11:46 ` [Qemu-devel] [PATCH 09/16] qemu-thread: introduce QemuLockCnt Paolo Bonzini
2016-01-15 15:12 [Qemu-devel] [PATCH 00/16] aio: first part of aio_context_acquire/release pushdown Paolo Bonzini
2016-01-15 15:12 ` [Qemu-devel] [PATCH 09/16] qemu-thread: introduce QemuLockCnt Paolo Bonzini
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=56B918F2.9020107@redhat.com \
--to=eblake@redhat.com \
--cc=pbonzini@redhat.com \
--cc=qemu-devel@nongnu.org \
--cc=stefanha@redhat.com \
/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 NNTP newsgroup(s).