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[86.183.162.145]) by smtp.gmail.com with ESMTPSA id c10sm313809wrb.92.2020.12.09.01.01.27 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Wed, 09 Dec 2020 01:01:28 -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: 4b2c993e-aec7-4513-b805-723463ff5767 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:reply-to:to:cc:references:in-reply-to:subject:date:message-id :mime-version:content-transfer-encoding:content-language :thread-index; bh=lPHsFue/8A1LiIQByTrkFvGuPpPc+9TVRioxM6O/VAg=; b=At0H2eMlJtYuHyiwGRn1V5FJ/KqvkdrT8F2HOndQqcQTq4hGXGFgwVDVzvF+hGAzrx boUsYoce/SWJgq9WJr3bavv/lvGpANzo2hvIkgRX+or0g3xsQRMmqbRoE03SzPcFtyic Uw/FEMyQtHnWihoHd+QjVrtfYjTZwwxflqWzHxRMu8QNRXBY8RDv9iGJ9E9tHudRBLBj 18w4C37HACVkUD53RQTwmSR2RkBhtbBpu552FhdVVYIRUSxSrmYV4HKYU+P3JIEt/kKP ne3PUMDz4XURmWiTdP03phRp2CTDCVoqcZjm2dOW+Yzt9z8PRQwB8HcOs3jkxJDy1tmD x+pw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:reply-to:to:cc:references:in-reply-to :subject:date:message-id:mime-version:content-transfer-encoding :content-language:thread-index; bh=lPHsFue/8A1LiIQByTrkFvGuPpPc+9TVRioxM6O/VAg=; b=qBRJkgDRNmcSKzM4NFbU6JXMoSgQv+ODCH3SuZZja3PX3OK2/+H+8m8NBuoT+w20IF 0VXPXY2SHjmNfLruM2ux43SHqiHGi8Z+TC0IJKLroqSewdhDScymJcRBWDEI40iQxoln WPTNqzHPLf5/LSVg/c4LUD4xlwqTqSyfx622RihUTFOeDVaulM/ROFHKJ9ppbZD6GsXy GoDBLA5f/TaeDUl96fqYV21n6gLAb3VJGOSBGLwtLSSM5mQF8VyvBLPrWCVBN9QBjUph drdUcKpNPkGq/hq9BXfWYAAF4MtAPhsqPoQGUm5vRzkC08KbwkVYhw+vQSPPvHqmKbhB CzyQ== X-Gm-Message-State: AOAM5321btbcNFpcalRJTLMrQDyI8ppaQBbyueET2b4nTFcCFJ+M5l6h S83R3+gGXQMsw+gxiWc4DbE= X-Google-Smtp-Source: ABdhPJyBN3Sy+Tpt0p2o3pXIxEp154Y4tLbSJFjl1TU1q0idH9o0QKXV0L3RmcXPQyhNrdCJYd9mpQ== X-Received: by 2002:a5d:660c:: with SMTP id n12mr1462599wru.291.1607504488891; Wed, 09 Dec 2020 01:01:28 -0800 (PST) From: Paul Durrant X-Google-Original-From: "Paul Durrant" Reply-To: To: "'Oleksandr'" Cc: "'Jan Beulich'" , "'Oleksandr Tyshchenko'" , "'Stefano Stabellini'" , "'Julien Grall'" , "'Volodymyr Babchuk'" , "'Andrew Cooper'" , "'George Dunlap'" , "'Ian Jackson'" , "'Wei Liu'" , "'Julien Grall'" , 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> <57bfc007-e400-6777-0075-827daa8acf0e@gmail.com> In-Reply-To: <57bfc007-e400-6777-0075-827daa8acf0e@gmail.com> Subject: RE: [PATCH V3 17/23] xen/ioreq: Introduce domain_has_ioreq_server() Date: Wed, 9 Dec 2020 09:01:27 -0000 Message-ID: <0d7201d6ce09$e13dce80$a3b96b80$@xen.org> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Mailer: Microsoft Outlook 16.0 Content-Language: en-gb Thread-Index: AQKk0D4Qme59XF0a0h96d36zIOxDhQIE/k2jAQvf44kCfV5qfQHp2KBNAqVQolsB+TCoJqfxvSbg > -----Original Message----- > From: Oleksandr > Sent: 08 December 2020 20:17 > 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 > Subject: Re: [PATCH V3 17/23] xen/ioreq: Introduce = domain_has_ioreq_server() >=20 >=20 > On 08.12.20 21:43, Paul Durrant wrote: >=20 > Hi Paul >=20 > >> -----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 =3D=3D 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. This is not relevant to the domain that the emulator is running in; it's = concerning the domains which the emulator is servicing. How many of = those are there? > 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... >=20 The helper may be one line but there is more to the patch than that. I = still think you could just walk the array in the helper rather than = keeping a running occupancy count. Paul