Then memset sounds good to me. No reason to over complicate things if it doesn't make a difference (or even hurts).
Gabe Joel Hestness wrote: > I have also tested using this loop. For a reasonably large file being > read, using the loop executes 300k fewer simulated instructions (~6% > of the readfile execution) than using memset. On the other hand, the > simulation time of the readfile call using memset was actually 0.4s > quicker (~5%) than using the loop. The simulated system still needs > to do a pagetable walk and mapping for each page regardless of the > implementation. So, my conclusion was that it doesn't make a > perceptible difference in performance, and the use of memset abstracts > away from possible problems with strided accesses using a static page > size. > > Joel > > > On Mon, Aug 9, 2010 at 12:50 PM, Ali Saidi <sa...@umich.edu > <mailto:sa...@umich.edu>> wrote: > > > > > On 2010-08-09 12:13:59, Nathan Binkert wrote: > > > > > How is this not a possible issue for every isa? We're talking > about touching 256kB of data. That shouldn't take very long. We've > beaten this to death, it's time to just call it done and move on. > If we're that concerned just do: > for (int x = 0; x < sizeof(buf); x += 512) > buf[x] = 0; > > It improves the speed by three orders of magnitude, doesn't > require and ifdef and will work on everything that doesn't have a > unbelievably small page size. > > > - Ali > > > ----------------------------------------------------------- > This is an automatically generated e-mail. To reply, visit: > http://reviews.m5sim.org/r/121/#review154 > ----------------------------------------------------------- > > > On 2010-08-09 10:35:49, Joel Hestness wrote: > > > > ----------------------------------------------------------- > > This is an automatically generated e-mail. To reply, visit: > > http://reviews.m5sim.org/r/121/ > > ----------------------------------------------------------- > > > > (Updated 2010-08-09 10:35:49) > > > > > > Review request for Default. > > > > > > Summary > > ------- > > > > util/m5/m5.c: in readfile(), added memset to touch all pages - > ensure they are in the page table > > > > This problem is caused by Linux demand paging. If the pages are > not yet mapped in the page table, the M5 utility does not know the > physical memory address in the simulated system to which it is > sending the file read from the host machine. > > > > > > Diffs > > ----- > > > > util/m5/m5.c a75564db03c3 > > > > Diff: http://reviews.m5sim.org/r/121/diff > > > > > > Testing > > ------- > > > > This fixes the functionality for x86, where the problem was > first encountered. I have also tested the utility for Alpha. The > simulated system executes approximately 10% more instructions > during the readfile operation due to the memset, but the > simulation time required for this is still marginal. Using memset > provides an ISA independent solution compared to buffer accesses > that use a page-sized stride. > > > > > > Thanks, > > > > Joel > > > > > > > > > -- > Joel Hestness > PhD Student, Computer Architecture > Dept. of Computer Science, University of Texas - Austin > http://www.cs.utexas.edu/~hestness > <http://www.cs.utexas.edu/%7Ehestness> > ------------------------------------------------------------------------ > > _______________________________________________ > m5-dev mailing list > m5-dev@m5sim.org > http://m5sim.org/mailman/listinfo/m5-dev > _______________________________________________ m5-dev mailing list m5-dev@m5sim.org http://m5sim.org/mailman/listinfo/m5-dev
