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Date: Thu, 3 May 2007 14:25:02 -0700 (PDT) From: david@...g.hm To: David Schwartz <davids@...master.com> cc: linux-kernel@...r.kernel.org Subject: RE: scheduling oddity on 2.6.20.3 stock On Thu, 3 May 2007, David Schwartz wrote: >> I needed to recompress some files from .bz2 to .gz so I setup a script to >> do >> >> bunzip2 -c $file.bz2 |gzip -9 >$file.gz >> >> I expected that the two CPU heavy processes would end up on different >> cpu's and spend a little time shuffling data between the two cpu's on a >> system (dual core opteron) >> >> however, instead what I find is that each process is getting 50% of one >> cpu while the other cpu is 97% idle. > > That would only be possible if the compression/decompression block size is > small compared to the maximum pipe buffer size. I suspect the reverse is the > case. > > It would be interesting to write an intermediate process that basically > enlarged the pipe buffers and see if that changed anything. Basically, the > intermediate process would allocate a large buffer (16MB or so) and fill it > from 'bunzip2' while draining it to 'gzip' in a non-blocking way (unless the > buffer was full/empty, of course). hmm, how about bunzip2 -c $file.bz2 |dd bs=8m |gzip -9 >$file.gz should that work? David Lang - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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