linux-kernel - Re: [PATCH 2/7] xen/events: don't unmask an event channel when an eoi is pending

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Date:   Mon, 8 Feb 2021 11:21:02 +0100
From:   Jürgen Groß <jgross@...e.com>
To:     Jan Beulich <jbeulich@...e.com>
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        stable@...r.kernel.org, Julien Grall <julien@....org>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/7] xen/events: don't unmask an event channel when an eoi
 is pending

On 08.02.21 11:06, Jan Beulich wrote:
> On 06.02.2021 11:49, Juergen Gross wrote:
>> @@ -1798,6 +1818,29 @@ static void mask_ack_dynirq(struct irq_data *data)
>>   	ack_dynirq(data);
>>   }
>>   
>> +static void lateeoi_ack_dynirq(struct irq_data *data)
>> +{
>> +	struct irq_info *info = info_for_irq(data->irq);
>> +	evtchn_port_t evtchn = info ? info->evtchn : 0;
>> +
>> +	if (VALID_EVTCHN(evtchn)) {
>> +		info->eoi_pending = true;
>> +		mask_evtchn(evtchn);
>> +	}
>> +}
>> +
>> +static void lateeoi_mask_ack_dynirq(struct irq_data *data)
>> +{
>> +	struct irq_info *info = info_for_irq(data->irq);
>> +	evtchn_port_t evtchn = info ? info->evtchn : 0;
>> +
>> +	if (VALID_EVTCHN(evtchn)) {
>> +		info->masked = true;
>> +		info->eoi_pending = true;
>> +		mask_evtchn(evtchn);
>> +	}
>> +}
>> +
>>   static int retrigger_dynirq(struct irq_data *data)
>>   {
>>   	evtchn_port_t evtchn = evtchn_from_irq(data->irq);
>> @@ -2023,8 +2066,8 @@ static struct irq_chip xen_lateeoi_chip __read_mostly = {
>>   	.irq_mask		= disable_dynirq,
>>   	.irq_unmask		= enable_dynirq,
>>   
>> -	.irq_ack		= mask_ack_dynirq,
>> -	.irq_mask_ack		= mask_ack_dynirq,
>> +	.irq_ack		= lateeoi_ack_dynirq,
>> +	.irq_mask_ack		= lateeoi_mask_ack_dynirq,
>>   
>>   	.irq_set_affinity	= set_affinity_irq,
>>   	.irq_retrigger		= retrigger_dynirq,
>>
> 
> Unlike the prior handler the two new ones don't call ack_dynirq()
> anymore, and the description doesn't give a hint towards this
> difference. As a consequence, clear_evtchn() also doesn't get
> called anymore - patch 3 adds the calls, but claims an older
> commit to have been at fault. _If_ ack_dynirq() indeed isn't to
> be called here, shouldn't the clear_evtchn() calls get added
> right here?

There was clearly too much time between writing this patch and looking
at its performance impact. :-(

Somehow I managed to overlook that I just introduced the bug here. This
OTOH explains why there are not tons of complaints with the current
implementation. :-)

Will merge patch 3 into this one.


Juergen

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