From: Matthew Wilcox <email@example.com> To: "Paul E. McKenney" <firstname.lastname@example.org> Cc: Andrea Parri <email@example.com>, Will Deacon <firstname.lastname@example.org>, email@example.com, firstname.lastname@example.org, email@example.com, Benjamin Herrenschmidt <firstname.lastname@example.org>, Arnd Bergmann <email@example.com>, David Laight <David.Laight@ACULAB.COM>, Alan Stern <firstname.lastname@example.org>, Peter Zijlstra <email@example.com> Subject: Re: [PATCH] docs/memory-barriers.txt: Enforce heavy ordering for port I/O accesses Date: Tue, 27 Nov 2018 11:22:34 -0800 Message-ID: <20181127192234.GF10377@bombadil.infradead.org> (raw) In-Reply-To: <20181127184021.GS4170@linux.ibm.com> On Tue, Nov 27, 2018 at 10:40:21AM -0800, Paul E. McKenney wrote: > On Mon, Nov 26, 2018 at 08:33:49PM +0100, Andrea Parri wrote: > > On Mon, Nov 26, 2018 at 04:52:14PM +0000, Will Deacon wrote: > > > David Laight explains: > > > > > > | A long time ago there was a document from Intel that said that > > > | inb/outb weren't necessarily synchronised wrt memory accesses. > > > | (Might be P-pro era). However no processors actually behaved that > > > | way and more recent docs say that inb/outb are fully ordered. > > > > No intention to diminish David Laight's authority of course, but I would > > have really appreciated a reference to these "recent docs" (section, pg. > > or the like, especially if a reference manual...) here... > > I would be inclined to cut Will a break given the research for his > recent talk on this topic, but it would be good to get an ack from > someone from Intel. And memory-model patches require an ack or better > in any case. ;-) Here's a quote from Section 18.6 of volume 1 of the Software Developer Manual, November 2018 edition: When the I/O address space is used instead of memory-mapped I/O, the situation is different in two respects: • The processor never buffers I/O writes. Therefore, strict ordering of I/O operations is enforced by the processor. (As with memory-mapped I/O, it is possible for a chip set to post writes in certain I/O ranges.) • The processor synchronizes I/O instruction execution with external bus activity (see Table 18-1). Table 18-1 says that in* delays execution of the current instruction until completion of pending stores, and out* delays execution of the _next_ instruction until completion of both pending stores and the current store.
next prev parent reply index Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-11-26 16:52 Will Deacon 2018-11-26 19:33 ` Andrea Parri 2018-11-27 18:40 ` Paul E. McKenney 2018-11-27 19:22 ` Matthew Wilcox [this message] 2018-11-26 19:42 ` Paul E. McKenney
Reply instructions: You may reply publicly to this message via plain-text email using any one of the following methods: * Save the following mbox file, import it into your mail client, and reply-to-all from there: mbox Avoid top-posting and favor interleaved quoting: https://en.wikipedia.org/wiki/Posting_style#Interleaved_style * Reply using the --to, --cc, and --in-reply-to switches of git-send-email(1): git send-email \ --in-reply-to=20181127192234.GF10377@bombadil.infradead.org \ --firstname.lastname@example.org \ --cc=David.Laight@ACULAB.COM \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ --email@example.com \ --firstname.lastname@example.org \ /path/to/YOUR_REPLY https://kernel.org/pub/software/scm/git/docs/git-send-email.html * If your mail client supports setting the In-Reply-To header via mailto: links, try the mailto: link
Linux-Doc Archive on lore.kernel.org Archives are clonable: git clone --mirror https://lore.kernel.org/linux-doc/0 linux-doc/git/0.git # If you have public-inbox 1.1+ installed, you may # initialize and index your mirror using the following commands: public-inbox-init -V2 linux-doc linux-doc/ https://lore.kernel.org/linux-doc \ email@example.com public-inbox-index linux-doc Example config snippet for mirrors Newsgroup available over NNTP: nntp://nntp.lore.kernel.org/org.kernel.vger.linux-doc AGPL code for this site: git clone https://public-inbox.org/public-inbox.git