-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 02/23/2015 04:17 PM, Maciej W. Rozycki wrote: > On Sat, 21 Feb 2015, Andy Lutomirski wrote: > >>> Additionally I believe long-executing FPU instructions (i.e. >>> transcendentals) can take advantage of continuing to execute in >>> parallel where the context has already been switched rather >>> than stalling an eager FPU context switch until the FPU >>> instruction has completed. >> >> It seems highly unlikely to me that a slow FPU instruction can >> retire *after* a subsequent fxsave, which would need to happen >> for this to work. > > I meant something else -- a slow FPU instruction can retire after a > task has been switched where the FP context has been left intact, > i.e. in the lazy FP context switching case, where only the MMU > context and GPRs have been replaced.
I don't think that's true, because changing the MMU context and GPRs also includes changing the instruction pointer, and changing over the execution to the new task. After a context switch, the instructions from the old task are no longer in the pipeline. - -- All rights reversed -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQEcBAEBAgAGBQJU65noAAoJEM553pKExN6DyVQH+gJDWuHyoFtgKFyELFi+tTGb vB/9uR267N4Hxu0D3kedhX9HNJwBtcs1rXm++p+r4RXpz2+gl/HxihoL8v1qk4zy 1lAa5se8T5hUL7MCsD5nOIs2ca3HAGwOFtVXrjvJQ6dSCCVD/SuqJC49ENc5Nd3M 1FcW4jg+MlQ2TNJoi4QRBllmxUFffACzv8M3VWVigIibMGqrOXXSraHp0k1hFFOE LeL122JKVp7YhVj5Dx7qx1DPUkT24RT9ip1f9r5DkxFmHwdCcY31WzT4asArqHb4 uwK8LVcpTax30VHghqy8KUBVKO5h7pHvdhTYSaoLWdUJfNFJ+8Hw5sDMfPdjN2k= =6lA5 -----END PGP SIGNATURE----- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
