Mailing List Archive

[PATCH 4/5] xen/events: unmask a fifo event channel only if it was masked
Unmasking an event channel with fifo events channels being used can
require a hypercall to be made, so try to avoid that by checking
whether the event channel was really masked.

Suggested-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
---
drivers/xen/events/events_fifo.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/xen/events/events_fifo.c b/drivers/xen/events/events_fifo.c
index 243e7b6d7b96..f60c5a9ec833 100644
--- a/drivers/xen/events/events_fifo.c
+++ b/drivers/xen/events/events_fifo.c
@@ -236,6 +236,9 @@ static bool clear_masked_cond(volatile event_word_t *word)

w = *word;

+ if (!(w & (1 << EVTCHN_FIFO_MASKED)))
+ return true;
+
do {
if (w & (1 << EVTCHN_FIFO_PENDING))
return false;
--
2.26.2
Re: [PATCH 4/5] xen/events: unmask a fifo event channel only if it was masked [ In reply to ]
On 22.10.2020 09:42, Juergen Gross wrote:
> --- a/drivers/xen/events/events_fifo.c
> +++ b/drivers/xen/events/events_fifo.c
> @@ -236,6 +236,9 @@ static bool clear_masked_cond(volatile event_word_t *word)
>
> w = *word;
>
> + if (!(w & (1 << EVTCHN_FIFO_MASKED)))
> + return true;

Maybe better move this ...

> do {
> if (w & (1 << EVTCHN_FIFO_PENDING))
> return false;
>

... into the loop, above this check?

Jan
Re: [PATCH 4/5] xen/events: unmask a fifo event channel only if it was masked [ In reply to ]
On 22.10.20 09:55, Jan Beulich wrote:
> On 22.10.2020 09:42, Juergen Gross wrote:
>> --- a/drivers/xen/events/events_fifo.c
>> +++ b/drivers/xen/events/events_fifo.c
>> @@ -236,6 +236,9 @@ static bool clear_masked_cond(volatile event_word_t *word)
>>
>> w = *word;
>>
>> + if (!(w & (1 << EVTCHN_FIFO_MASKED)))
>> + return true;
>
> Maybe better move this ...
>
>> do {
>> if (w & (1 << EVTCHN_FIFO_PENDING))
>> return false;
>>
>
> ... into the loop, above this check?

Yes, that should be better.


Juergen