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Re: [Qemu-devel] [PATCH 09/16] qemu-thread: introduce QemuLockCnt
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH 09/16] qemu-thread: introduce QemuLockCnt |
Date: |
Mon, 8 Feb 2016 15:38:42 -0700 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.0 |
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 <address@hidden>
> ---
> 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 <address@hidden>
> + */
> +#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
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- [Qemu-devel] [PATCH 03/16] aio: introduce aio_poll_internal, (continued)
- [Qemu-devel] [PATCH 03/16] aio: introduce aio_poll_internal, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 02/16] aio: do not really acquire/release the main AIO context, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 01/16] aio: introduce aio_context_in_iothread, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 06/16] qemu-thread: introduce QemuRecMutex, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 05/16] iothread: release AioContext around aio_poll, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 07/16] aio: convert from RFifoLock to QemuRecMutex, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 08/16] aio: rename bh_lock to list_lock, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 04/16] aio: only call aio_poll_internal from iothread, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 09/16] qemu-thread: introduce QemuLockCnt, Paolo Bonzini, 2016/02/08
- Re: [Qemu-devel] [PATCH 09/16] qemu-thread: introduce QemuLockCnt,
Eric Blake <=
- [Qemu-devel] [PATCH 12/16] aio: tweak walking in dispatch phase, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 11/16] qemu-thread: optimize QemuLockCnt with futexes on Linux, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 14/16] aio-win32: remove walking_handlers, protecting AioHandler list with list_lock, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 13/16] aio-posix: remove walking_handlers, protecting AioHandler list with list_lock, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 10/16] aio: make ctx->list_lock a QemuLockCnt, subsuming ctx->walking_bh, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 16/16] aio: push aio_context_acquire/release down to dispatching, Paolo Bonzini, 2016/02/08
- [Qemu-devel] [PATCH 15/16] aio: document locking, Paolo Bonzini, 2016/02/08