From mboxrd@z Thu Jan 1 00:00:00 1970 Mime-Version: 1.0 (Apple Message framework v752.3) In-Reply-To: References: Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed Message-Id: <73906362-D2E4-4388-813D-CB066864BF57@telus.net> Content-Transfer-Encoding: 7bit From: Paul Lalonde Subject: Re: [9fans] GCC/G++: some stress testing Date: Mon, 3 Mar 2008 18:17:00 -0800 To: Fans of the OS Plan 9 from Bell Labs <9fans@cse.psu.edu> Topicbox-Message-UUID: 6e006924-ead3-11e9-9d60-3106f5b1d025 -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Mar 3, 2008, at 4:49 PM, erik quanstrom wrote: > really? to out-predict the cache hardware, you have to have pretty > complete knowlege of everything running on all cores and be pretty > good at guessing what will want scheduling next. not to mention, > you'd need to keep close tabs on which memory is cachable/wc/etc. On the flip side, ignoring the cache leads to algorithms whose working sets can't fit in cache, wasting a considerable amount of processing to cache misses. Being able to parameterize your algorithms to work comfortably in one or two ways of your cache can bring *huge* performance improvements without dropping to the traditional assembly. I'm arguing that being aware of the caches lets the system better schedule your work because you aren't preventing it from doing something smart. > > aren't these arguments for networked rather than shared memory > multiprocessors? Yes. Although I work for a company that prides itself on its cache coherence know-how, I'm very much a believer in networked multiprocessors, even on a chip. I like Cell better than Opteron, for example. They are harder to program up front, however, which causes difficulties in adoption. Flip-side, once you've overcome your startup hurdles the networked model seems to provide more predictable performance management. Paul > > - erik -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.3 (Darwin) iD8DBQFHzLEdpJeHo/Fbu1wRAkNNAKC54Me95evWld4cUlUb0Wd9NXQF7QCfZ9zn QZ5kn6JLfK3EXocNz+plF4c= =xSzm -----END PGP SIGNATURE-----