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Wed, 03 Feb 2021 11:01:00 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 1A247AF78; Wed, 3 Feb 2021 11:00:59 +0000 (UTC) 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: 71be47ef-49ca-4e16-b71b-4bc84dedfc28 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1612350059; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=q3KE9TfPPTGcvsD79BQ0xkUg5qvgl+n+GeEjBrtJUTQ=; b=ldc7uadkWkVhpHyEOxvGwOxb7RHboVcDmqoQYhWqS44mzA45woaJRIssi4zeuxMj1rPzV8 W6i2hfSx9O3GvRdgI+zG9tVg4pHJeUla8qM8LEj6TB3yfZudeRAIqRckd2EWWMTy7Z5zWw HjQ75RF+CZhB2XzHyeh6vmZR/Xx/Aps= To: Julien Grall , Dario Faggioli , =?UTF-8?Q?Anders_T=c3=b6rnqvist?= , xen-devel@lists.xenproject.org, Stefano Stabellini Cc: Jan Beulich , Andrew Cooper References: <207305e4e2998614767fdcc5ad83ced6de982820.camel@suse.com> <744ddde6-a228-82fc-76b9-401926d7963b@xen.org> <18ef4619-19ae-90d2-459c-9b5282b49176@codiax.se> <4760cbac-b006-78bc-b064-3265384f6707@xen.org> <311bb201bcacfd356f0c0b67856754eceae39e37.camel@suse.com> <7f2ec84a-9814-ffb1-0940-e936a80afbbb@xen.org> <501664dbdb736eaa4d9c05255dedfd7ad3e694fa.camel@suse.com> <1ab7ad80-c027-ffdd-8188-e1ab1fd53335@xen.org> From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= Subject: Re: Null scheduler and vwfi native problem Message-ID: <5ad8befd-75a1-4995-e0bb-e1a438f7556d@suse.com> Date: Wed, 3 Feb 2021 12:00:58 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <1ab7ad80-c027-ffdd-8188-e1ab1fd53335@xen.org> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="1lnwlIH2lKrIgSY5B9gyffH7R1kVJtffb" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --1lnwlIH2lKrIgSY5B9gyffH7R1kVJtffb Content-Type: multipart/mixed; boundary="ZTGhjvmEWTexT4YQaGjqlqe0yhO9njnuy"; protected-headers="v1" From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= To: Julien Grall , Dario Faggioli , =?UTF-8?Q?Anders_T=c3=b6rnqvist?= , xen-devel@lists.xenproject.org, Stefano Stabellini Cc: Jan Beulich , Andrew Cooper Message-ID: <5ad8befd-75a1-4995-e0bb-e1a438f7556d@suse.com> Subject: Re: Null scheduler and vwfi native problem References: <207305e4e2998614767fdcc5ad83ced6de982820.camel@suse.com> <744ddde6-a228-82fc-76b9-401926d7963b@xen.org> <18ef4619-19ae-90d2-459c-9b5282b49176@codiax.se> <4760cbac-b006-78bc-b064-3265384f6707@xen.org> <311bb201bcacfd356f0c0b67856754eceae39e37.camel@suse.com> <7f2ec84a-9814-ffb1-0940-e936a80afbbb@xen.org> <501664dbdb736eaa4d9c05255dedfd7ad3e694fa.camel@suse.com> <1ab7ad80-c027-ffdd-8188-e1ab1fd53335@xen.org> In-Reply-To: <1ab7ad80-c027-ffdd-8188-e1ab1fd53335@xen.org> --ZTGhjvmEWTexT4YQaGjqlqe0yhO9njnuy Content-Type: multipart/mixed; boundary="------------18CF0D851AD2BAB757E8F521" Content-Language: en-US This is a multi-part message in MIME format. --------------18CF0D851AD2BAB757E8F521 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 03.02.21 10:19, Julien Grall wrote: > Hi, >=20 > On 03/02/2021 07:31, Dario Faggioli wrote: >> On Tue, 2021-02-02 at 15:23 +0000, Julien Grall wrote: >>> In reality, it is probably still too early as a pCPU can be >>> considered >>> quiesced until a call to rcu_lock*() (such rcu_lock_domain()). >>> >> Well, yes, in theory, we could track down which is the first RCU read >> side crit. section on this path, and put the call right before that (i= f >> I understood what you mean). >=20 > Oh, that's not what I meant. This will indeed be far more complex than = I=20 > originally had in mind. >=20 > AFAIU, the RCU uses critical section to protect data. So the "entering"= =20 > could be used as "the pCPU is not quiesced" and "exiting" could be used= =20 > as "the pCPU is quiesced". >=20 > The concern with my approach is we would need to make sure that Xen=20 > correctly uses the rcu helpers. I know Juergen worked on that recently,= =20 > but I don't know whether this is fully complete. I think it is complete, but I can't be sure, of course. One bit missing (for catching some wrong uses of the helpers) is this patch: https://lists.xen.org/archives/html/xen-devel/2020-03/msg01759.html I don't remember why it hasn't been taken, but I think there was a specific reason for that. 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