220 40978 <1f8aee48-8a20-0f42-b180-bf1d31a47530@gmail.com> article Path: news.gmane.org!.POSTED!not-for-mail From: Anthony Williams Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Thread preemption inside RCU protected section Date: Mon, 12 Nov 2018 06:52:51 +0000 Lines: 45 Approved: news@gmane.org Message-ID: <1f8aee48-8a20-0f42-b180-bf1d31a47530@gmail.com> References: <88ff3707-f1d9-42ae-ac2d-3e926ff32350@isocpp.org> Reply-To: std-proposals@isocpp.org NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Trace: blaine.gmane.org 1542005450 21301 195.159.176.226 (12 Nov 2018 06:50:50 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Mon, 12 Nov 2018 06:50:50 +0000 (UTC) User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.3.0 To: std-proposals@isocpp.org Original-X-From: std-proposals+bncBD65DK5LTQNBBR6GUTPQKGQECD7UA7Y@isocpp.org Mon Nov 12 07:50:46 2018 Return-path: Envelope-to: gclcip-std-proposals@m.gmane.org Original-Received: from mail-wm1-f71.google.com ([209.85.128.71]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1gM63Z-0005Re-Gg for gclcip-std-proposals@m.gmane.org; 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[178.79.187.92]) by smtp.gmail.com with ESMTPSA id f68sm2795906wmd.15.2018.11.11.22.52.52 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 11 Nov 2018 22:52:52 -0800 (PST) Openpgp: preference=signencrypt Autocrypt: addr=anthony.ajw@gmail.com; prefer-encrypt=mutual; keydata= xsFNBFKLKCcBEACsieh8DThKfzIRYsUCdaZn6LHywphYGl/+Y0pDYqWvKgG0j00ril1WdCbj 8p/DTS9E+dYNZnhY3KyM1rhCGPUJ1jMtDZD5XhDWMKIFmVu5htNzs1/198IuPT6dnn0uY/Le cPmBYo9In/Xp5VRDTbjg0g2OnbCK+3Lg3C9f5b7Fb8kz/DlD8WNOBODRYz7JGjMakvBixoSk ECUMF1fFs2mG6trIl1W+90pr8dYL4KhRkew1SVnAkiICmCx+Lq7zEurkrQH98sVLzJdB7mAB 3u/DHU6otXS6S7O2+T8MdufvYVqILjAHpRyJP9k8Jbxh4X4bgwLwDDCIiFPiaXIcS2YZmGlV gQ/wHCCDP7mqu2RTnfaWGTqd98Ka2jvzQoGDQ7j80Fb+1GIldY5L/jTj6QbJrIZA94+qwGcA hH1+p8IajxjMzs9SzpwSNCDyqqpOGi/NduBvwyIvOPB9NCerMRmJg1EPNb6TKHyPMeWrmA+b gtdXb96H1gTKG9s2CPKI4SOsjQn7/mmIp9/XsroX/EYo/7n1mPUE8A6dEfLtlUbrXUIixvHg 7Ba/ao74Quv0T1BQi5PnAUU7UKwYz5B10PPWZerZSd3NZ1tupTYZsphYl+/QEIRM62nKVBvT uyjAx16E8ldMH+VIltxWn6uxFXMNHlQ/qYKgz9sva1LA1AY3/QARAQABzTZBbnRob255IFdp bGxpYW1zIDxhbnRob255QGp1c3Rzb2Z0d2FyZXNvbHV0aW9ucy5jby51az7CwX4EEwECACgC GyMGCwkIBwMCBh In-Reply-To: <88ff3707-f1d9-42ae-ac2d-3e926ff32350@isocpp.org> Content-Language: en-GB X-Original-Sender: anthony.ajw@gmail.com X-Original-Authentication-Results: mx.google.com; dkim=pass header.i=@gmail.com header.s=20161025 header.b="nTXwPXH/"; spf=pass (google.com: domain of anthony.ajw@gmail.com designates 209.85.220.41 as permitted sender) smtp.mailfrom=anthony.ajw@gmail.com; dmarc=pass (p=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Spam-Checked-In-Group: std-proposals@isocpp.org X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:40978 Archived-At: On 11/11/2018 21:34, Itaj Sherman wrote: > What happens if a user thread enters a section protected by a locked > rcu_reader instance, and gets preempted by the scheduler inside the > section?! Nothing. > When it wakes up, it supposedly continues to run inside the section. >=20 > Which means that all rcu protected objects used inside the section have > to be delayed for a long time until after the thread gets scheduled again= .. Yes. > I want to propose the following suggestion. I really am not sure if it=E2= =80=99s > feasible, it needs compiler and OS support that I=E2=80=99m not sure is a= lways > available. It is unnecessary. RCU is designed to cope with long grace periods before reclamation, precisely due to issues like this. At kernel level, you already have the ability to mark sections of code non-preemptable. At user level, this would require the ability to run code when the OS is preempting you (in order to remove the RCU read tag), which is against the very concept of preemption, so it is not implementable. Cheers, Anthony --=20 You received this message because you are subscribed to the Google Groups "= ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. To view this discussion on the web visit https://groups.google.com/a/isocpp= ..org/d/msgid/std-proposals/1f8aee48-8a20-0f42-b180-bf1d31a47530%40gmail.com= .. .