Zoltan Menyhart wrote on Monday, March 13, 2006 6:09 AM > I think we can do some accessed/dirty bit handler tuning. E.g. > in my patch (based on the Christoph's one entitled "Fix race in the > accessed/dirty bit handlers"), I think we gain a bit by: > > ... > - not testing the result of "cmpxchg" (we'll re-read the PTE and > compare it anyway) It occurs on me that you can do even more: you don't even need the 2nd load, move itc opportunistically before cmpxchg, then use data returned from cmpxchg and compare it to the first read. Oh, well, I suppose Tony has enough versions to jog around ;-) - Ken --- ./arch/ia64/kernel/ivt.S.orig 2006-03-13 15:39:36.745990157 -0800 +++ ./arch/ia64/kernel/ivt.S 2006-03-13 15:43:56.757705722 -0800 @@ -563,23 +563,12 @@ ENTRY(dirty_bit) or r25=_PAGE_D|_PAGE_A,r18 // set the dirty and accessed bits tbit.z p7,p6 = r18,_PAGE_P_BIT // Check present bit ;; +(p6) itc.d r25 // install updated PTE (p6) cmpxchg8.acq r26=[r17],r25,ar.ccv // Only update if page is present mov r24=PAGE_SHIFT<<2 ;; (p6) cmp.eq p6,p7=r26,r18 // Only compare if page is present ;; -(p6) itc.d r25 // install updated PTE - ;; - /* - * Tell the assemblers dependency-violation checker that the above "itc" instructions - * cannot possibly affect the following loads: - */ - dv_serialize_data - - ld8 r18=[r17] // read PTE again - ;; - cmp.eq p6,p7=r18,r25 // is it same as the newly installed - ;; (p7) ptc.l r16,r24 mov b0=r29 // restore b0 mov ar.ccv=r28 - : send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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