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Re: [Qemu-devel] [PATCH] replay: don't synchronize memory operations in
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH] replay: don't synchronize memory operations in replay mode |
Date: |
Tue, 17 Sep 2019 12:44:35 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 |
On 17/09/19 11:54, Pavel Dovgalyuk wrote:
> Commit 9458a9a1df1a4c719e24512394d548c1fc7abd22 added synchronization
> of vCPU and migration operations through calling run_on_cpu operation.
> However, in replay mode this synchronization is unneeded, because
> I/O and vCPU threads are already synchronized.
> This patch disables such synchronization for record/replay mode.
>
> Signed-off-by: Pavel Dovgalyuk <address@hidden>
> ---
> exec.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/exec.c b/exec.c
> index be8b2b7c06..a69745811f 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -3177,8 +3177,17 @@ static void tcg_log_global_after_sync(MemoryListener
> *listener)
> * by pushing the migration thread's memory read after the vCPU thread
> has
> * written the memory.
> */
> - cpuas = container_of(listener, CPUAddressSpace, tcg_as_listener);
> - run_on_cpu(cpuas->cpu, do_nothing, RUN_ON_CPU_NULL);
> + if (replay_mode == REPLAY_MODE_NONE) {
> + /*
> + * VGA can make calls to this function while updating the screen.
> + * In record/replay mode this causes a deadlock, because
> + * run_on_cpu waits for rr mutex. Therefore no races are possible
> + * in this case and no need for making run_on_cpu when
> + * record/replay is not enabled.
> + */
> + cpuas = container_of(listener, CPUAddressSpace, tcg_as_listener);
> + run_on_cpu(cpuas->cpu, do_nothing, RUN_ON_CPU_NULL);
> + }
> }
>
> static void tcg_commit(MemoryListener *listener)
>
Looks good.
Paolo