Kelly Hall <[EMAIL PROTECTED]> wrote: > > From: Pieter de Goeje <[EMAIL PROTECTED]> > > Subject: Re: "tar -c|gzip" faster than "tar -cz"?!? > > > > The tar|gzip command uses 18% less CPU and is 10% faster. It > > is clear the HDD is the bottleneck. > > Now it's clear to me :) > > This makes sense if tar is single-threaded: there's only one thread of > execution, and it can either be waiting on the disk, or compressing > data. With two processes, gzip can compress while tar blocks on disk > IO.
No. During my tests there was no physical disk I/O (the disk LED was *OFF* all the time). So tar certainly wasn't blocking on disk I/O. The difference in CPU time (and wall clock time) seems simply to be caused by different compression code. gzip is noticeably more efficient than libz, at least on the OS/processor combination where I tested it (Athlon64 with FreeBSD/i386 6.2-PRERELEASE). Depending on the type of data, the difference is between 25% and 40%. If the data is not compressible (like stuff from /dev/random, or already compressed files), it's only 25%. For very good compressible data (best case: /dev/null), the difference is 40%. Best regards Oliver -- Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing Dienstleistungen mit Schwerpunkt FreeBSD: http://www.secnetix.de/bsd Any opinions expressed in this message may be personal to the author and may not necessarily reflect the opinions of secnetix in any way. cat man du : where Unix geeks go when they die _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
