From: Leonardo Bras Soares Passos <leobras@redhat.com>
To: Juan Quintela <quintela@redhat.com>
Cc: qemu-devel <qemu-devel@nongnu.org>,
"Marcel Apfelbaum" <marcel.apfelbaum@gmail.com>,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
"Peter Xu" <peterx@redhat.com>, "Eric Blake" <eblake@redhat.com>,
"Philippe Mathieu-Daudé" <f4bug@amsat.org>,
"Yanan Wang" <wangyanan55@huawei.com>,
"Markus Armbruster" <armbru@redhat.com>,
"Eduardo Habkost" <eduardo@habkost.net>
Subject: Re: [PATCH v7 07/12] multifd: Prepare to send a packet without the mutex held
Date: Sat, 20 Aug 2022 04:27:26 -0300 [thread overview]
Message-ID: <CAJ6HWG540gasXXtEBU3QNKDzMdvH5jjDN-oz3CpFUBfN1qJX4g@mail.gmail.com> (raw)
In-Reply-To: <878rnk1nb8.fsf@secure.mitica>
On Fri, Aug 19, 2022 at 8:32 AM Juan Quintela <quintela@redhat.com> wrote:
>
> Leonardo Brás <leobras@redhat.com> wrote:
> > On Tue, 2022-08-02 at 08:39 +0200, Juan Quintela wrote:
> >> We do the send_prepare() and the fill of the head packet without the
> >> mutex held. It will help a lot for compression and later in the
> >> series for zero pages.
> >>
> >> Notice that we can use p->pages without holding p->mutex because
> >> p->pending_job == 1.
> >>
> >> Signed-off-by: Juan Quintela <quintela@redhat.com>
> >> ---
> >> migration/multifd.h | 2 ++
> >> migration/multifd.c | 11 ++++++-----
> >> 2 files changed, 8 insertions(+), 5 deletions(-)
> >>
> >> diff --git a/migration/multifd.h b/migration/multifd.h
> >> index a67cefc0a2..cd389d18d2 100644
> >> --- a/migration/multifd.h
> >> +++ b/migration/multifd.h
> >> @@ -109,7 +109,9 @@ typedef struct {
> >> /* array of pages to sent.
> >> * The owner of 'pages' depends of 'pending_job' value:
> >> * pending_job == 0 -> migration_thread can use it.
> >> + * No need for mutex lock.
> >> * pending_job != 0 -> multifd_channel can use it.
> >> + * No need for mutex lock.
> >> */
> >> MultiFDPages_t *pages;
> >>
> >> diff --git a/migration/multifd.c b/migration/multifd.c
> >> index 09a40a9135..68fc9f8e88 100644
> >> --- a/migration/multifd.c
> >> +++ b/migration/multifd.c
> >> @@ -663,6 +663,8 @@ static void *multifd_send_thread(void *opaque)
> >> p->flags |= MULTIFD_FLAG_SYNC;
> >> p->sync_needed = false;
> >> }
> >> + qemu_mutex_unlock(&p->mutex);
> >> +
> >
> > If it unlocks here, we will have unprotected:
> > for (int i = 0; i < p->pages->num; i++) {
> > p->normal[p->normal_num] = p->pages->offset[i];
> > p->normal_num++;
> > }
> >
> > And p->pages seems to be in the mutex-protected area.
> > Should it be ok?
>
> From the documentation:
>
> /* array of pages to sent.
> * The owner of 'pages' depends of 'pending_job' value:
> * pending_job == 0 -> migration_thread can use it.
> * No need for mutex lock.
> * pending_job != 0 -> multifd_channel can use it.
> * No need for mutex lock.
> */
> MultiFDPages_t *pages;
>
> So, it is right.
Oh, right. I missed that part earlier .
>
> > Also, under that we have:
> > if (p->normal_num) {
> > ret = multifd_send_state->ops->send_prepare(p, &local_err);
> > if (ret != 0) {
> > qemu_mutex_unlock(&p->mutex);
> > break;
> > }
> > }
> >
> > Calling mutex_unlock() here, even though the unlock already happened before,
> > could cause any issue?
>
> Good catch. Never got an error there.
>
> Removing that bit.
Thanks!
Best regards,
Leo
>
> > Best regards,
>
>
> Thanks, Juan.
>
next prev parent reply other threads:[~2022-08-20 7:29 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-02 6:38 [PATCH v7 00/12] Migration: Transmit and detect zero pages in the multifd threads Juan Quintela
2022-08-02 6:38 ` [PATCH v7 01/12] multifd: Create page_size fields into both MultiFD{Recv, Send}Params Juan Quintela
2022-08-11 8:10 ` [PATCH v7 01/12] multifd: Create page_size fields into both MultiFD{Recv,Send}Params Leonardo Brás
2022-08-13 15:41 ` Juan Quintela
2022-08-02 6:38 ` [PATCH v7 02/12] multifd: Create page_count fields into both MultiFD{Recv, Send}Params Juan Quintela
2022-08-11 8:10 ` [PATCH v7 02/12] multifd: Create page_count fields into both MultiFD{Recv,Send}Params Leonardo Brás
2022-08-02 6:38 ` [PATCH v7 03/12] migration: Export ram_transferred_ram() Juan Quintela
2022-08-11 8:11 ` Leonardo Brás
2022-08-13 15:36 ` Juan Quintela
2022-08-02 6:38 ` [PATCH v7 04/12] multifd: Count the number of bytes sent correctly Juan Quintela
2022-08-11 8:11 ` Leonardo Brás
2022-08-19 9:35 ` Juan Quintela
2022-08-02 6:39 ` [PATCH v7 05/12] migration: Make ram_save_target_page() a pointer Juan Quintela
2022-08-11 8:11 ` Leonardo Brás
2022-08-19 9:51 ` Juan Quintela
2022-08-20 7:14 ` Leonardo Bras Soares Passos
2022-08-22 21:35 ` Juan Quintela
2022-08-02 6:39 ` [PATCH v7 06/12] multifd: Make flags field thread local Juan Quintela
2022-08-11 9:04 ` Leonardo Brás
2022-08-19 10:03 ` Juan Quintela
2022-08-20 7:24 ` Leonardo Bras Soares Passos
2022-08-23 13:00 ` Juan Quintela
2022-08-02 6:39 ` [PATCH v7 07/12] multifd: Prepare to send a packet without the mutex held Juan Quintela
2022-08-11 9:16 ` Leonardo Brás
2022-08-19 11:32 ` Juan Quintela
2022-08-20 7:27 ` Leonardo Bras Soares Passos [this message]
2022-08-02 6:39 ` [PATCH v7 08/12] multifd: Add capability to enable/disable zero_page Juan Quintela
2022-08-11 9:29 ` Leonardo Brás
2022-08-19 11:36 ` Juan Quintela
2022-08-02 6:39 ` [PATCH v7 09/12] migration: Export ram_release_page() Juan Quintela
2022-08-11 9:31 ` Leonardo Brás
2022-08-02 6:39 ` [PATCH v7 10/12] multifd: Support for zero pages transmission Juan Quintela
2022-09-02 13:27 ` Leonardo Brás
2022-11-14 12:09 ` Juan Quintela
2022-10-25 9:10 ` chuang xu
2022-11-14 12:10 ` Juan Quintela
2022-08-02 6:39 ` [PATCH v7 11/12] multifd: Zero " Juan Quintela
2022-09-02 13:27 ` Leonardo Brás
2022-11-14 12:20 ` Juan Quintela
2022-11-14 12:27 ` Juan Quintela
2022-08-02 6:39 ` [PATCH v7 12/12] So we use multifd to transmit zero pages Juan Quintela
2022-09-02 13:27 ` Leonardo Brás
2022-11-14 12:30 ` Juan Quintela
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