[llvm-dev] RFC: EfficiencySanitizer

[Hal Finkel via llvm-dev]

----- Original Message -----

> From: "Qin Zhao" <zhaoqin at google.com>
> To: "Hal Finkel" <hfinkel at anl.gov>
> Cc: "Derek Bruening" <bruening at google.com>,
> efficiency-sanitizer at google.com, "llvm-dev"
> <llvm-dev at lists.llvm.org>
> Sent: Thursday, April 21, 2016 12:48:20 PM
> Subject: Re: [llvm-dev] RFC: EfficiencySanitizer

> > Will this technology allow us to pinpoint specific accesses that
> > generally have high latency (i.e. generally are cache misses)? This
> > information is useful for programmers, and is also useful as an
> > input to loop unrolling, instruction scheduling, and the like on
> > ooo
> > cores.
> 

> Won't hardware performance counter tell you which accesses are
> delinquent accesses?
Yes, for the particular system on which you're running. The question is, as the (effective) cache size changes (either because you're running more threads per core, socket, etc. or as you run across different architectures), can you say where the cache-miss hot-spots will be? 

-Hal 

> The tools here are trying to provide more information and hopefully
> some insight of the performance problem.

> For example, if we can tell that the working set of an application is
> slightly bigger than the L3 cache, developers would be able to take
> the right action to improve the performance.

> We are welcome any suggestions about how the information can be used,
> or what information should be collected.

> Qin

> > -Hal
> 

> > >
> 
> > > *Dead store detection*: this tool identifies dead stores
> 
> > > (write-after-write patterns with no intervening read) as well as
> 
> > > redundant stores (writes of the same value already in memory).
> > > Xref
> 
> > > the Deadspy paper from CGO 2012.
> 
> > >
> 
> > >
> 
> > > *Single-reference*: this tool identifies data cache lines brought
> > > in
> 
> > > but only read once. These could be candidates for non-temporal
> 
> > > loads.
> 
> > >
> 
> > >
> 
> > > ====================
> 
> > > EfficiencySanitizer
> 
> > > ====================
> 
> > >
> 
> > >
> 
> > > We are proposing the name EfficiencySanitizer, or "esan" for
> > > short,
> 
> > > to refer to this suite of dynamic instrumentation tools for
> 
> > > improving program efficiency. As we have a number of different
> > > tools
> 
> > > that share quite a bit of their implementation we plan to
> > > consider
> 
> > > them sub-tools under the EfficiencySanitizer umbrella, rather
> > > than
> 
> > > adding a whole bunch of separate instrumentation and runtime
> > > library
> 
> > > components.
> 
> > >
> 
> > >
> 
> > > While these tools are not addressing correctness issues like
> > > other
> 
> > > sanitizers, they will be sharing a lot of the existing sanitizer
> 
> > > runtime library support code. Furthermore, users are already
> 
> > > familiar with the sanitizer brand, and it seems better to extend
> 
> > > that concept rather than add some new term.
> 
> > >
> 
> > >
> 
> > > _______________________________________________
> 
> > > LLVM Developers mailing list
> 
> > > llvm-dev at lists.llvm.org
> 
> > > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> 
> > >
> 

> > --
> 
> > Hal Finkel
> 
> > Assistant Computational Scientist
> 
> > Leadership Computing Facility
> 
> > Argonne National Laboratory
> 

> > --
> 
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> 
> > To view this discussion on the web visit
> > https://groups.google.com/a/google.com/d/msgid/efficiency-sanitizer/19928798.1837.1461205693345.JavaMail.hfinkel%40sapling5.localdomain
> > .
> 

-- 

Hal Finkel 
Assistant Computational Scientist 
Leadership Computing Facility 
Argonne National Laboratory 
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