On 02/12/2015 14:04, Christian Borntraeger wrote: >> > Do you gain much over the simpler >> > >> > vcpu->run->s.regs.gprs[14] = vcpu->arch.sie_block->gg14; >> > vcpu->run->s.regs.gprs[15] = vcpu->arch.sie_block->gg15; >> > > Its just legacy code from the old days. > There is a difference, but it seems to a missed opportunity from gcc > > vcpu->arch.sie_block->gg14 = vcpu->run->s.regs.gprs[14]; > 839c: e3 30 f0 b8 00 04 lg %r3,184(%r15) > 83a2: e3 10 32 40 00 04 lg %r1,576(%r3) > 83a8: e3 20 30 80 00 04 lg %r2,128(%r3) > 83ae: e3 20 21 b8 00 04 lg %r2,440(%r2) > 83b4: e3 20 10 a0 00 24 stg %r2,160(%r1) > vcpu->arch.sie_block->gg15 = vcpu->run->s.regs.gprs[15]; > 83ba: e3 10 32 40 00 04 lg %r1,576(%r3) > 83c0: e3 20 30 80 00 04 lg %r2,128(%r3) > 83c6: e3 20 21 c0 00 04 lg %r2,448(%r2) > 83cc: e3 20 10 a8 00 24 stg %r2,168(%r1) > > gcc seems to reuse and reload %r2 and %r3, maybe register pressure. More likely to be -fno-strict-aliasing. :( Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
