Re: [win-pv-devel] [PATCH] Avoid making hypercalls in the SyncWorker DPC

[Fabio Fantoni <fabio.fantoni@xxxxxxx>]

Il 20/11/2014 17:25, Paul Durrant ha scritto:
> The code has to run with interrupts disabled on all CPUs apart from 0 to
> corale them across a suspend/resume. Making hypercalls from within that
> code is thus incompatible with re-populating the hypercall table on resume
> since it transpites then Xen writes each byte in the page to 0xcc (int 3)
> before actually setting up the hypercall thunks. The only hypercall that the
> code was actually making was a SCHEDOP_yield and this is trivially replaced
> by an _mm_pause intrinsic which calls through to SCHEDOP_yield in the
> VMEXIT handler.
Thanks for the patch, I tested it, 3 save/restore without crash for now 
and I not saw any regression, I'll report you if I'll see other crash.
There is another problem with the save/restore on windows that is 
driving me crazy for months:
with qxl vga all works good except after save/restore that make domU 
"freeze" for 2-3 minutes on spice connect (always first time and 
occasional the others), on windows shutdown/reboot and probably other 
operations.
I'm unable to found the exactly cause of that, is there a way to know if 
is caused by something unexpected in windows pv drivers or other xen 
particular things in xen save/restore? (for example "interrupts disabled 
on all CPUs apart from 0 to corale them across a suspend/resume" if I 
understand good).
Thanks for any reply and sorry for my bad english.

> Signed-off-by: Paul Durrant<paul.durrant@xxxxxxxxxx>
> ---
>   src/xenbus/sync.c | 14 +++++++-------
>   1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/src/xenbus/sync.c b/src/xenbus/sync.c
> index 41ecbf9..78b5bef 100644
> --- a/src/xenbus/sync.c
> +++ b/src/xenbus/sync.c
> @@ -151,7 +151,7 @@ SyncWorker(
>               break;
>   
>           if (SyncContext.DisableInterrupts[Cpu] == InterruptsDisabled) {
> -            SchedYield();
> +            _mm_pause();
>               KeMemoryBarrier();
>   
>               continue;
> @@ -171,7 +171,7 @@ SyncWorker(
>               Attempts = 0;
>               while (SyncContext.Sequence == Sequence &&
>                      SyncContext.CompletionCount < CpuCount) {
> -                SchedYield();
> +                _mm_pause();
>                   KeMemoryBarrier();
>   
>                   if (++Attempts > 1000) {
> @@ -213,7 +213,7 @@ SyncWorker(
>   
>               while (SyncContext.Sequence == Sequence &&
>                      SyncContext.CompletionCount < CpuCount) {
> -                SchedYield();
> +                _mm_pause();
>                   KeMemoryBarrier();
>               }
>   
> @@ -268,7 +268,7 @@ SyncCapture(
>       InterlockedIncrement(&SyncContext.CompletionCount);
>   
>       while (SyncContext.CompletionCount < CpuCount) {
> -        SchedYield();
> +        _mm_pause();
>           KeMemoryBarrier();
>       }
>   
> @@ -305,7 +305,7 @@ again:
>   
>       Attempts = 0;
>       while (SyncContext.CompletionCount < CpuCount) {
> -        SchedYield();
> +        _mm_pause();
>           KeMemoryBarrier();
>   
>           if (++Attempts > 1000) {
> @@ -366,7 +366,7 @@ SyncEnableInterrupts(
>       InterlockedIncrement(&SyncContext.CompletionCount);
>   
>       while (SyncContext.CompletionCount < CpuCount) {
> -        SchedYield();
> +        _mm_pause();
>           KeMemoryBarrier();
>       }
>   
> @@ -400,7 +400,7 @@ SyncRelease(
>       InterlockedIncrement(&SyncContext.CompletionCount);
>   
>       while (SyncContext.CompletionCount < CpuCount) {
> -        SchedYield();
> +        _mm_pause();
>           KeMemoryBarrier();
>       }
>   
> -- 2.1.1

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