Date: Mon, 11 Apr 2016 14:48:03 +0200 From: Luigi Rizzo <rizzo@iet.unipi.it> To: Slawa Olhovchenkov <slw@zxy.spb.ru> Cc: freebsd-current <freebsd-current@freebsd.org> Subject: Re: stall-free memory reads ? (possibly stale) ? Message-ID: <CA%2BhQ2%2BiMDV4JRS2bhA-r3=2QmcFhpJB60OPA3YpTQfmP2TQyPg@mail.gmail.com> In-Reply-To: <20160408212237.GA6614@zxy.spb.ru> References: <20160408162416.GA94343@onelab2.iet.unipi.it> <20160408212237.GA6614@zxy.spb.ru>
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thank you, much appreciated. On Fri, Apr 8, 2016 at 11:22 PM, Slawa Olhovchenkov <slw@zxy.spb.ru> wrote: > 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 > > -- -----------------------------------------+------------------------------- Prof. Luigi RIZZO, rizzo@iet.unipi.it . Dip. di Ing. dell'Informazione http://www.iet.unipi.it/~luigi/ . Universita` di Pisa TEL +39-050-2217533 . via Diotisalvi 2 Mobile +39-338-6809875 . 56122 PISA (Italy) -----------------------------------------+-------------------------------
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