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Miller" , Jakub Kicinski References: <20210206104932.29064-1-jgross@suse.com> <7aaeeb3d-1e1b-6166-84e9-481153811b62@suse.com> <6f547bb5-777a-6fc2-eba2-cccb4adfca87@xen.org> <0d623c98-a714-1639-cc53-f58ba3f08212@suse.com> <28399fd1-9fe8-f31a-6ee8-e78de567155b@xen.org> <1831964f-185e-31bb-2446-778f2c18d71b@suse.com> From: Julien Grall Message-ID: Date: Mon, 8 Feb 2021 12:16:41 +0000 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <1831964f-185e-31bb-2446-778f2c18d71b@suse.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/02/2021 12:14, Jürgen Groß wrote: > On 08.02.21 11:40, Julien Grall wrote: >> Hi Juergen, >> >> On 08/02/2021 10:22, Jürgen Groß wrote: >>> On 08.02.21 10:54, Julien Grall wrote: >>>> ... I don't really see how the difference matter here. The idea is >>>> to re-use what's already existing rather than trying to re-invent >>>> the wheel with an extra lock (or whatever we can come up). >>> >>> The difference is that the race is occurring _before_ any IRQ is >>> involved. So I don't see how modification of IRQ handling would help. >> >> Roughly our current IRQ handling flow (handle_eoi_irq()) looks like: >> >> if ( irq in progress ) >> { >>    set IRQS_PENDING >>    return; >> } >> >> do >> { >>    clear IRQS_PENDING >>    handle_irq() >> } while (IRQS_PENDING is set) >> >> IRQ handling flow like handle_fasteoi_irq() looks like: >> >> if ( irq in progress ) >>    return; >> >> handle_irq() >> >> The latter flow would catch "spurious" interrupt and ignore them. So >> it would handle nicely the race when changing the event affinity. > > Sure? Isn't "irq in progress" being reset way before our "lateeoi" is > issued, thus having the same problem again? Sorry I can't parse this. And I think we want to keep > the lateeoi behavior in order to be able to control event storms. I didn't (yet) suggest to remove lateeoi. I only suggest to use a different workflow to handle the race with vCPU affinity. Cheers, -- Julien Grall