Messages in this thread |  | | Date | Tue, 9 Oct 2001 09:49:24 -0400 | Subject | Re: Context switch times | From | (bill davidsen) |
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In article <200110090455.f994tNB22322@vindaloo.ras.ucalgary.ca> rgooch@ras.ucalgary.ca asked:
| Hm. Perhaps when I did my tests (where I noticed a penalty), we didn't | have lazy FPU saving. Now we disable the FPU, and restore state when | we trap, right? | | I do note this comment in arch/i386/kernel/process.c: | * We fsave/fwait so that an exception goes off at the right time | * (as a call from the fsave or fwait in effect) rather than to | * the wrong process. Lazy FP saving no longer makes any sense | * with modern CPU's, and this simplifies a lot of things (SMP | * and UP become the same). | | So what exactly is the difference between our "delayed FPU restore | upon trap" (which I think of as lazy FPU saving), and the "lazy FP" | saving in the comments?
We always save the FPU, but only restore it when/if it is going to be used. And obviously we don't want to save it if it hasn't been used, since it wasn't restored...
-- bill davidsen <davidsen@tmr.com> "If I were a diplomat, in the best case I'd go hungry. In the worst case, people would die." -- Robert Lipe - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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