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Tue, 08 Dec 2020 20:17:03 +0000 (UTC) Received: by mail-lj1-x242.google.com with SMTP id a1so20442708ljq.3 for ; Tue, 08 Dec 2020 12:17:03 -0800 (PST) Received: from [192.168.1.7] ([212.22.223.21]) by smtp.gmail.com with ESMTPSA id 129sm3313925lfo.43.2020.12.08.12.17.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 08 Dec 2020 12:17:01 -0800 (PST) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: c0d09c8f-303e-4305-b729-833d2c61df6a DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-transfer-encoding:content-language; bh=HjN+rS4v9m2c0PQGwpM1swajT+DtylVzRjuh32YTpSg=; b=MTvB2lIh+q69m1zntUlL9zABjWhq8rfXDZtLJBr8qp4Ur1saBRsSfkbmc8K4K5eqTI q0uHzijYrMZrTfXNCoKbt5YUvLoRsT0YhDHpBSsv+GjjnGp4TyA3tzKlu4/CevwAGQAH oVyuoYuy6fJMCzjsDZBlg6DdGMsGKUwv5ZTIgnoWe6kfXhRXHY9SALD4yVBWWqc8L69C r8xEwsJWqVK28GNPxixzY76fsC3oyhSW7FEdZqU+/CL5CR9+a/8LVIU/SRl3cmd9VXud u8ZTSvSpAAFLkHSlu9psXSUCsRwIPSHtsLfvZphfzkakAldpLV+aGinr2lAkkTQ2Q/9o LeOA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding :content-language; bh=HjN+rS4v9m2c0PQGwpM1swajT+DtylVzRjuh32YTpSg=; b=FQKa27AZza2vcBM8+QfmwJ7HN7X6/TgnW8v5GmZ3fYWHfNGokivP6HkbFJg/nHsqpf rHXDoJjXwLiOxDihk+NZI84QITKPbHeXSThRf0XuYhiYTo3rLWJnumX33vgTVrWVTh7T jFsaMrMATllpiua8HluIlwwwIxng/kZYsLUDzuL7mJfG50dT40IT+KE74fb1Y+KtBUKt URhU14ehzWax7voMfoWH80O+5I3DP1VANb3D3W1SsfJSjNzpRH+KvL6YggM0Td4gREjr rJ6tW6RSNZrxFpGAUKkHkaWAotpGMGpKQ1NaBBp3Tg6DZpjtHJ89giOAey3wwjmrX7r4 DWlw== X-Gm-Message-State: AOAM530cY5stEUq3ratKCmgPKyT61XOn0BqQPijBDYalZ5DGQj6+c00G mg+bYrzyT78szOWmPgTwpkhJ69wWAWW8yQ== X-Google-Smtp-Source: ABdhPJzbpxEywi/5uHMqUt1RniGQlNgWxGgbf+PuWG/YPxAxEUjeMoaGAzdgeDceVIJeHUeIKLOoLQ== X-Received: by 2002:a2e:58f:: with SMTP id 137mr1647786ljf.469.1607458622449; Tue, 08 Dec 2020 12:17:02 -0800 (PST) Subject: Re: [PATCH V3 17/23] xen/ioreq: Introduce domain_has_ioreq_server() To: paul@xen.org Cc: 'Jan Beulich' , 'Oleksandr Tyshchenko' , 'Stefano Stabellini' , 'Julien Grall' , 'Volodymyr Babchuk' , 'Andrew Cooper' , 'George Dunlap' , 'Ian Jackson' , 'Wei Liu' , 'Julien Grall' , xen-devel@lists.xenproject.org References: <1606732298-22107-1-git-send-email-olekstysh@gmail.com> <1606732298-22107-18-git-send-email-olekstysh@gmail.com> <3bb4c3b5-a46a-ba31-292f-5c6ba49fa9be@suse.com> <6026b7f3-ae6e-f98f-be65-27d7f729a37f@gmail.com> <18bfd9b1-3e6a-8119-efd0-c82ad7ae681d@gmail.com> <0d6c01d6cd9a$666326c0$33297440$@xen.org> From: Oleksandr Message-ID: <57bfc007-e400-6777-0075-827daa8acf0e@gmail.com> Date: Tue, 8 Dec 2020 22:16:55 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <0d6c01d6cd9a$666326c0$33297440$@xen.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US On 08.12.20 21:43, Paul Durrant wrote: Hi Paul >> -----Original Message----- >> From: Oleksandr >> Sent: 08 December 2020 16:57 >> To: Paul Durrant >> Cc: Jan Beulich ; Oleksandr Tyshchenko ; Stefano >> Stabellini ; Julien Grall ; Volodymyr Babchuk >> ; Andrew Cooper ; George Dunlap >> ; Ian Jackson ; Wei Liu ; Julien Grall >> ; xen-devel@lists.xenproject.org >> Subject: Re: [PATCH V3 17/23] xen/ioreq: Introduce domain_has_ioreq_server() >> >> >> Hi Paul. >> >> >> On 08.12.20 17:33, Oleksandr wrote: >>> On 08.12.20 17:11, Jan Beulich wrote: >>> >>> Hi Jan >>> >>>> On 30.11.2020 11:31, Oleksandr Tyshchenko wrote: >>>>> --- a/xen/include/xen/ioreq.h >>>>> +++ b/xen/include/xen/ioreq.h >>>>> @@ -55,6 +55,20 @@ struct ioreq_server { >>>>> uint8_t bufioreq_handling; >>>>> }; >>>>> +/* >>>>> + * This should only be used when d == current->domain and it's not >>>>> paused, >>>> Is the "not paused" part really relevant here? Besides it being rare >>>> that the current domain would be paused (if so, it's in the process >>>> of having all its vCPU-s scheduled out), does this matter at all?do >>>> any extra actionsdo any extra actions >>> No, it isn't relevant, I will drop it. >>> >>> >>>> Apart from this the patch looks okay to me, but I'm not sure it >>>> addresses Paul's concerns. Iirc he had suggested to switch back to >>>> a list if doing a swipe over the entire array is too expensive in >>>> this specific case. >>> We would like to avoid to do any extra actions in >>> leave_hypervisor_to_guest() if possible. >>> But not only there, the logic whether we check/set >>> mapcache_invalidation variable could be avoided if a domain doesn't >>> use IOREQ server... >> >> Are you OK with this patch (common part of it)? > How much of a performance benefit is this? The array is small to simply counting the non-NULL entries should be pretty quick. I didn't perform performance measurements on how much this call consumes. In our system we run three domains. The emulator is in DomD only, so I would like to avoid to call vcpu_ioreq_handle_completion() for every Dom0/DomU's vCPUs if there is no real need to do it. On Arm vcpu_ioreq_handle_completion() is called with IRQ enabled, so the call is accompanied with corresponding irq_enable/irq_disable. These unneeded actions could be avoided by using this simple one-line helper... -- Regards, Oleksandr Tyshchenko