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Re: [qemu-s390x] [PATCH v1 for-2-12 06/15] s390x/flic: factor out inject

From: David Hildenbrand
Subject: Re: [qemu-s390x] [PATCH v1 for-2-12 06/15] s390x/flic: factor out injection of floating interrupts
Date: Tue, 12 Dec 2017 16:17:17 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0

On 12.12.2017 15:29, Cornelia Huck wrote:
> On Tue, 12 Dec 2017 15:13:46 +0100
> Christian Borntraeger <address@hidden> wrote:
>> On 12/12/2017 02:49 PM, Cornelia Huck wrote:
>>> One thing I noticed: You removed the caching of the flic (in the old
>>> kvm inject routine), and you generally do more qom invocations (first,
>>> to find the common flic; then, to translate to the qemu or kvm flic).
>>> Not sure if this might be a problem (probably not).  
>> Is any of these calls on a potential fast path (e.g. guest without adapter
>> interrupts)? If yes, then QOM is a no-go since it is really slow.
> At least the new airq interface was using QOM without caching before.
> It's basically about any interrupt; but otoh we are (for kvm) in
> userspace already. Caching the flic and just keeping the casting to the
> specialized flic might be ok (I'd guess that the lookup is the slowest
> path.)

Please note that the lookup is already cached in s390_get_flic(); That
should be sufficient, as it does the expensive lookup. One cache should
be enough, no?

The other conversions should be cheap (and already were in place in a
couple of places before).




David / dhildenb

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