Date: Wed, 18 Mar 2015 14:04:52 +0300 From: Solar Designer <solar@...nwall.com> To: john-dev@...ts.openwall.com Subject: Re: [GSoC] building JtR for MIC On Wed, Mar 18, 2015 at 01:38:45PM +0300, Solar Designer wrote: > On Wed, Mar 18, 2015 at 05:27:45PM +0800, Lei Zhang wrote: > > 2. There're two kind of numbers in the output, real and virtual. What's their difference? > > This is in the FAQ: > > Q: What are the "real" and "virtual" c/s rates as reported by "--test" > (on Unix-like operating systems)? > A: These correspond to real and virtual (processor) time, respectively. > The two results would differ when the system is under other load, with > the "virtual" c/s rate indicating roughly what you could expect to get > from the same machine if it were not loaded. > > ... but this FAQ entry is outdated and needs to be revised. As written, > it applies to single-threaded builds only (I wrote it before we > introduced OpenMP support). Clearly, the numbers also differ greatly in > multi-threaded builds. When running a multi-threaded build on an > otherwise idle system, the "real" speed will be roughly equal to the > "virtual" speed times the number of threads. I've just revised this FAQ entry to be: Q: What are the "real" and "virtual" c/s rates as reported by "--test"? A: These correspond to real and virtual (processor) time, respectively. When running single-threaded, the two results are normally almost the same, but the "real" c/s rate becomes smaller when the system is under other load, with the "virtual" c/s rate indicating roughly what you could expect to get from the same system if it were not loaded. When running multi-threaded, the "real" c/s rate is normally much higher than the "virtual" c/s rate, with the latter roughly indicating performance of one thread on an otherwise idle system. Alexander
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