Date: Mon, 18 Jan 2016 20:13:00 +0000 (UTC) From: Benjamin Kaduk <bjk@FreeBSD.org> To: doc-committers@freebsd.org, svn-doc-all@freebsd.org, svn-doc-head@freebsd.org Subject: svn commit: r48055 - head/en_US.ISO8859-1/htdocs/news/status Message-ID: <201601182013.u0IKD0An089439@repo.freebsd.org>
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Author: bjk Date: Mon Jan 18 20:13:00 2016 New Revision: 48055 URL: https://svnweb.freebsd.org/changeset/doc/48055 Log: Add sendfile entry from glebius Modified: head/en_US.ISO8859-1/htdocs/news/status/report-2015-10-2015-12.xml Modified: head/en_US.ISO8859-1/htdocs/news/status/report-2015-10-2015-12.xml ============================================================================== --- head/en_US.ISO8859-1/htdocs/news/status/report-2015-10-2015-12.xml Mon Jan 18 18:42:46 2016 (r48054) +++ head/en_US.ISO8859-1/htdocs/news/status/report-2015-10-2015-12.xml Mon Jan 18 20:13:00 2016 (r48055) @@ -3631,4 +3631,114 @@ </task> </help> </project> + + <project cat='kern'> + <title>Sendfile(2) Improvements</title> + + <contact> + <person> + <name> + <given>Gleb</given> + <common>Smirnoff</common> + </name> + <email>glebius@FreeBSD.org</email> + </person> + </contact> + + <links> + <url href="https://svnweb.FreeBSD.org/base?view=revision&revision=293439">Commit to Head</url> + <url href="http://www.slideshare.net/facepalmtarbz2/new-sendfile-in-english">Slides</url>; + <url href="https://events.yandex.ru/lib/talks/2682/">Presentation (in Russian)</url> + </links> + + <body> + <p>The <tt>sendfile(2)</tt> system call was introduced in + 1998 as an alternative to a traditional + <tt>read(2)</tt>/<tt>write(2)</tt> loop, speeding up server + performance by a factor of ten at the time. Since it was adopted + by all major operating systems, it is now used by any serious web + server software. Wherever there is high traffic, there is + <tt>sendfile(2)</tt> under the hood.</p> + + <p>Now, with &os; 11, we are making the next revolutinary step + in serving traffic. <tt>sendfile(2)</tt> no longer blocks waiting + on disk I/O. Instead, it immediately returns control to the + application, performing the necessary I/O in the background. The + original <tt>sendfile(2)</tt> waited for the disk read operation + to complete and then put the data that was read into the socket, + then returned to userspace. If a web server serves thousands of + clients, with thousands of requests, in order to avoid stalls it + needed to spawn extra contexts from which to run + <tt>sendfile(2)</tt>. Alternatively, it could use special tricks + like the <tt>SF_NODISKIO</tt> flag that forces + <tt>sendfile(2)</tt> to serve only content that is cached in + memory. Now, these tricks are in the past, and a web server can + simply use <tt>sendfile(2)</tt> as it would use <tt>write(2)</tt>, + withouth any extra care. The new sendfile cuts out the overhead + of extra contexts, short writes, and extra syscalls to prepopulate + the cache, bringing performance to new level.</p> + + <p>The new syscall is built on top of two new features + introduced in the kernel. The first one is an asynchronous VM + pager interface, and the corresponding + <tt>VOP_GETPAGES_ASYNC()</tt> file system method for UFS. The + second one is the concept of "not ready" data in + sockets. When <tt>sendfile(2)</tt> is called, first + VOP_GETPAGES_ASYNC() is called, which dispatches I/O requests for + completion. Then, buffers with pages to be populated are put into + the socket buffer, but flagged as not-yet-ready. Then control + immediately returns to the application. When the I/O is finished, + the buffers are marked as ready, and the socket is activated to + continue transmission.</p> + + <p>Additional features of the new sendfile are new flags that + provide an application with extra control over the transmitted + content. Now it is possible to prevent caching of content in + memory, which is useful when it is known that the content is + unlikely to be reused any time soon. In such cases, it is better + to let the associated storage be freed, rather than puting the + data in cache. It is also possible to specify a readahead with + every syscall, if the application can predict client behavior.</p> + + <p>The new <tt>sendfile(2)</tt> is a drop-in replacement, API + and ABI compatible with old one. Applications do not even need to + recompile in order to benefit from the new implementation.</p> + + <p>This work is a joint effort between two companies: NGINX, + Inc., and Netflix. There were many people involved in the + project. At its initial stage, when no code was yet written, the + idea of such an asynchronous drop-in replacement was discussed + amongst &a.glebius;, &a.scottl;, &a.kib;, &a.adrian;, and Igor + Sysoev. The initial prototype was coded by Gleb under the + supervision of Kostik on the VM parts of patch, and under constant + pressure from Igor, who demanded that nginx be capable of running + with the new <tt>sendfile(2)</tt> with no modifications. The + prototype demonstrated good performance and stability and quickly + went into Netflix production in late 2014. During 2015, the code + matured and continued serving production traffic at Netflix. + &a.scottl;, &a.rrs;, &a.emax;, and &a.gallatin; added their + contributions to the code.</p> + + <p>Now we are releasing the code behind our success to the + &os; community, making it available to all &os; users + worldwide!</p> + </body> + + <sponsor> + Netflix + </sponsor> + + <sponsor> + NGINX, Inc. + </sponsor> + + <help> + <task> + <p><tt>SSL_sendfile()</tt> — an extension to the new + <tt>sendfile(2)</tt> that allows uploading session keys to the + kernel, and then using <tt>sendfile(2)</tt> on an SSL-enabled + socket.</p> + </task> + </help> + </project> </report>
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