Date: Sat, 9 Apr 2016 00:22:37 +0300 From: Slawa Olhovchenkov <slw@zxy.spb.ru> To: Luigi Rizzo <rizzo@iet.unipi.it> Cc: freebsd-current@freebsd.org Subject: Re: stall-free memory reads ? (possibly stale) ? Message-ID: <20160408212237.GA6614@zxy.spb.ru> In-Reply-To: <20160408162416.GA94343@onelab2.iet.unipi.it> References: <20160408162416.GA94343@onelab2.iet.unipi.it>
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On Fri, Apr 08, 2016 at 06:24:16PM +0200, Luigi Rizzo wrote: > Hi, > I have an application with two threads sharing a memory variable, > one continuously writing, one continuously reading. > > Because of the way my system works, the reader can tolerate reading > stale data, but it should not stall on memory reads (the line > is on the local cache for the reader, just might be invalidated). > > I was wondering if there is some way (either generic or > x86-specific, either simple or convoluted, possibly using > multiple versions of the shared variable in different cache > lines) to make sure that reads never stalls (or, equivalently, > let me read stale values from the cache) ? > > I have done some experiments and on a single-socket machines > the stallled reads take some 50ns; on a dual socket machine > the stall penalty grows to about 200ns. Can this link help to you? https://tu-dresden.de/die_tu_dresden/zentrale_einrichtungen/zih/forschung/projekte/benchit/2015_ICPP_authors_version.pdf
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