- Add Q3 reports on static code analysis [1] and CAM locking [2]
Submitted by: uqs [1], mav [2]
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Gabor Pali
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Notes:
svn2git
2020-12-08 03:00:23 +00:00
svn path=/head/; revision=42634
1 changed files with 129 additions and 1 deletions
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@ -19,13 +19,19 @@
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<!-- XXX: keep updating the number of entries -->
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<p>Thanks to all the reporters for the excellent work! This report
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contains 1 entries and we hope you enjoy reading it.</p>
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contains 3 entries and we hope you enjoy reading it.</p>
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<!-- XXX: set date for the next set of submissions -->
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<p>The deadline for submissions covering between October and
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December 2013 is not yet decided.</p>
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</section>
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<category>
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<name>proj</name>
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<description>Projects</description>
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</category>
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<category>
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<name>kern</name>
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@ -60,4 +66,126 @@
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framework and <tt>crypto(4)</tt>.</p>
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</body>
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</project>
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<project cat='proj'>
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<title>Static Code Analysis</title>
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<contact>
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<person>
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<name>
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<given>Ulrich</given>
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<common>Spoerlein</common>
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</name>
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<email>uqs@FreeBSD.org</email>
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</person>
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</contact>
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<links>
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<url href="http://scan.coverity.com/">Coverity Scan</url>
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<url href="http://scan.freebsd.your.org/">Clang Static Analyzer Scan for &os;</url>
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<url href="http://clang-analyzer.llvm.org/">Clang Static Analyzer Home Page</url>
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</links>
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<body>
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<p>With our own (old and unstable) instance of Coverity Prevent
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gone, we have now fully transitioned to the Scan project run by
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Coverity (see links), which Open Source projects can use to
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learn about possible defects in their source code.</p>
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<p>We also continue to run our code base through the Static
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Analyzer that is shipped with Clang/LLVM. It cannot track the
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state of the code over time, but has the benefit that everyone
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can use it without any special setup. See the home page at the
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links section for more information on the Clang Static Analyzer
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project in general, and head over to the &os; Clang Static
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Analyzer Scan page (see links) to see those possible defects (no
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signup required).</p>
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<p>We are looking for a co-admin for both of these projects to
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increase the bus-factor and the chance of survival for these
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services. Fame and fortune await!</p>
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</body>
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<help>
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<task>Maybe turn on email reports for new defects to the internal
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list of &os; developers.</task>
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<task>Find co-admin.</task>
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<task>Fix the defects reported by Coverity and Clang.</task>
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</help>
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</project>
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<project cat='kern'>
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<title>GEOM Direct Dispatch and Fine-Grained CAM Locking</title>
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<contact>
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<person>
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<name>
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<given>Alexander</given>
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<common>Motin</common>
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</name>
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<email>mav@FreeBSD.org</email>
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</person>
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</contact>
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<links>
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<url href="http://svnweb.freebsd.org/base/projects/camlock/">Project SVN branch</url>
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<url href="http://people.freebsd.org/~mav/camlock_patches/">Project patches</url>
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</links>
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<body>
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<p>Last year's high-performance storage vendors reported
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performance bottleneck in &os; block storage subsystem, limiting
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peak performance around 300-500K IOPS. While that is still more
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then enough for average systems, detailed investigation has
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shown number of places that require radical improvement.
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Unmapped I/O support implemented early this year already
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improved I/O performance by about 30% and moved more accents
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toward GEOM and CAM subsystems scalability. Fixing these issues
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was the goal of this project.</p>
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<p>The existing GEOM design assumed the most of I/O handling to be
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done by only two kernel threads (<tt>g_up()</tt> and
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<tt>g_down()</tt>). That simplified locking in some cases, but
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limited potential SMP scalability and created additional
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scheduler overhead. This project introduces concept of direct
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I/O dispatch into GEOM for cases where it is know to be safe and
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efficient. That implies marking some of GEOM consumers and
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providers with one or two new flags, declaring situations when
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direct function call can be used instead of normal request
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queuing. That allows to avoid any context switches inside GEOM
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for the most widely used topologies, simultaneously processing
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multiple I/Os from multiple calling threads.</p>
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<p>Having GEOM passing through multiple concurrent calls down to
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the underlying layers exposed major lock congestion in CAM. In
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existing CAM design all devices connected to the same ATA/SCSI
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controller are sharing single lock, which can be quite busy due
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to multiple controller hardware accesses and/or code logic.
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Experiments have shown that applying only above GEOM direct
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dispatch changes burns up to 60% of system CPU time or even more
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in attempts to obtain these locks by multiple callers, killing
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any benefits of GEOM direct dispatch. To overcome that new
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fine-grained CAM locking design was implemented. It implies
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splitting big per-SIM locks into several smaller ones: per-LUN
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locks, per-bus locks, queue locks, etc. After these changes
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remaining per-SIM lock protects only controller driver
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internals, reducing lock congestion down to acceptable level and
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allowing to keep compatibility with existing drivers.</p>
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<p>Together GEOM and CAM changes twice increase peak I/O rate,
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reaching up to 1,000,000 IOPS on contemporary hardware.</p>
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<p>The changes were tested by number of people and are going to be
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committed into &os; <tt>head</tt> and merged to
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<tt>stable/10</tt> after the end of &os; 10.0 release cycle.</p>
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<p>The project is sponsored by iXsystems, Inc.</p>
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</body>
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<help>
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<task>More reviews, more stability and performance tests.</task>
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</help>
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</project>
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</report>
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