On 2/11/25 11:43, Sohil Mehta wrote: > + /* > + * Modern CPUs are generally expected to have a sane fast string > + * implementation. However, the BIOS may disable it on certain CPUs > + * via the architectural FAST_STRING bit. > + */ > + if (IS_ENABLED(CONFIG_X86_64) && (c->x86 == 6 || c->x86 > 15)) > + set_cpu_cap(c, X86_FEATURE_REP_GOOD); I'm not sure the BIOS comment is helpful here. Also, at this point, let's just make the check >=6 (or the >=PPRO equivalent). It will only matter if *all* of these are true: 1. Someone has a 64-bit capable P4 that powers on 2. They're running a 64-bit mainline kernel 3. String copy is *actually* slower than the alternative 4. They are performance sensitive enough to notice We don't even know the answer to #3 for sure. Let's just say what we're doing in a comment: /* Assume that any 64-bit CPU has a good implementation */
