From: Nicolai Stange <nstange@suse.de>
To: speck@linutronix.de
Subject: [MODERATED] Re: [RFC PATCH 4/6] kvm: handle host mode irqs 4
Date: Sun, 29 Jul 2018 22:00:22 +0200 [thread overview]
Message-ID: <87fu01ak2x.fsf_-_@suse.de> (raw)
In-Reply-To: <ebe39f37-b80d-557f-c608-4788eb1ff175@redhat.com> (speck for Paolo Bonzini's message of "Fri, 27 Jul 2018 11:55:56 +0200")
speck for Paolo Bonzini <speck@linutronix.de> writes:
> On 27/07/2018 11:17, speck for Nicolai Stange wrote:
>> speck for Peter Zijlstra <speck@linutronix.de> writes:
>>
>>> On Wed, Jul 25, 2018 at 01:45:32PM +0200, speck for Nicolai Stange wrote:
>>>> So if nobody objects, I'll go with what Paolo proposed at [1]: replace
>>>> the 'kernel_mode_irq_gen' counter with a latch flag and set that for any
>>>> irq (but NMIs for a start).
>>>
>>> Well, the reason I suggested the other counters, is to avoid adding yet
>>> another dirty cacheline to IRQs. Since we're already touching those
>>> fields for most interrupts anyway.. might as well extend them to cover
>>> what we need instead of adding more dirty lines.
>>>
>>
>> Ah I see, that makes sense of course.
>>
>> I think there are two possible ways forward:
>>
>> 1.) Squeeze that new "kvm_cpu_l1tf_flush_l1d" latch flag into
>> irq_cpustat_t. irq_cpustat_t is arch-specific and there
>> is some room in its first cacheline, for example inserting
>> up to four bytes right after ->irq_tlb_count wouldn't move
>> anything critical out.
>>
>> 2.) Make the non-do_IRQ() irqs, i.e. smp_apic_timer_interrupt() & Co,
>> call kstat_incr_irqs_this_cpu() and adapt arch_irq_stat_cpu()
>> accordingly. Let vmx use struct kernel_stat ->irqs_sum as a
>> irq generation counter as before.
>>
>> Pros 1.)
>> - Easy to implement.
>> - Doesn't rely on irq_domain drivers.
>>
>> Cons 1.)
>> - Extra store from do_IRQ() irqs in comparison to 2.)
>> - That "kvm_cpu_l1tf_flush_l1d" flag doesn't really qualify
>> as an "IRQ stat" and it might be surprising to have it there.
>
> There's precedent for this, for example __softirq_pending. In fact you
> could reduce __softirq_pending to an u16 and not increase the size of
> irq_cpustat_t, since there are <16 softirqs.
Perfect, thanks!
Nicolai
next prev parent reply other threads:[~2018-07-29 20:06 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-23 9:54 [MODERATED] [RFC PATCH 0/6] kvm: handle host mode irqs 0 Nicolai Stange
2018-07-21 20:16 ` [MODERATED] [RFC PATCH 1/6] kvm: handle host mode irqs 1 Nicolai Stange
2018-07-21 20:25 ` [MODERATED] [RFC PATCH 2/6] kvm: handle host mode irqs 2 Nicolai Stange
2018-07-21 20:35 ` [MODERATED] [RFC PATCH 3/6] kvm: handle host mode irqs 3 Nicolai Stange
2018-07-22 9:35 ` [MODERATED] [RFC PATCH 4/6] kvm: handle host mode irqs 4 Nicolai Stange
2018-07-23 15:40 ` [MODERATED] " Andi Kleen
2018-07-24 5:58 ` Nicolai Stange
2018-07-24 14:12 ` Andi Kleen
2018-07-24 14:39 ` Paolo Bonzini
2018-07-24 15:21 ` Peter Zijlstra
2018-07-25 11:45 ` Nicolai Stange
2018-07-27 7:45 ` Peter Zijlstra
2018-07-27 9:17 ` Nicolai Stange
2018-07-27 9:55 ` Paolo Bonzini
2018-07-29 20:00 ` Nicolai Stange [this message]
2018-07-22 11:06 ` [MODERATED] [RFC PATCH 5/6] kvm: handle host mode irqs 5 Nicolai Stange
2018-07-22 11:38 ` [MODERATED] [RFC PATCH 6/6] kvm: handle host mode irqs 6 Nicolai Stange
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