Pádraig Brady <[EMAIL PROTECTED]> wrote: > I was surprised that dd did memcpy() by default, > which one can see using: > > ltrace -e memcpy dd if=/dev/zero of=/dev/null count=10 > > Now if you specify bs=512 for example > a memcpy() is not done, which seems inconsistent to me. > > What about the attached patch to not do a > memory copy in any of the combinations where > ibs = obs, and conversions are not done? > > cheers, > Pádraig. >>From 3bf7a447aa0b2339915cb5abe4d17919224c88dc Mon Sep 17 00:00:00 2001 > From: =?utf-8?q?P=C3=A1draig=20Brady?= <[EMAIL PROTECTED]> > Date: Thu, 20 Nov 2008 22:49:02 +0000 > Subject: [PATCH] Don't do unneccesary memory copies in dd.
That looks fine. You're welcome to push it, but please first amend it to use the following log message instead, which starts with "PROGNAME: " and mentions the affected function name. ---------- dd: avoid unnecessary memory copies * src/dd.c (scanargs): When not otherwise required (e.g. for conversion), use two-buffer mode only when the input and output buffer sizes differ. Before, some of the most basic invocations of dd, e.g., dd < in > out, would unnecessarily use separate buffers and perform unnecessary memcpy operations. ---------- I was disappointed to see no performance improvement. But it's not too surprising: this affects dd only with a block size that's so low (512) that the cost of the memcpy is lost in the noise of the read/write syscalls. Maybe on some small/old CPU it actually does make a difference. _______________________________________________ Bug-coreutils mailing list Bug-coreutils@gnu.org http://lists.gnu.org/mailman/listinfo/bug-coreutils
