search for: gru_flush_cach

...calls smp_mb and not mb() I couldn't figure out why - original patches did mb() there. Outside core kernel - drm_cache_flush_clflush, drm_clflush_sg, drm_clflush_virt_range. Then there's gru_start_instruction in drivers/misc/sgi-gru/. But otherwise drivers/misc/sgi-gru/ calls clflush in gru_flush_cache without calling mb() - this could be a bug. Looking at all users, it seems that only mwait_idle calls smp_mb, around clflush, others call mb(). So at least as a first step, maybe it makes sense to scope this down somewhat by changing mwait_idle to call mb() and then optimizing __smp_mb instead...

...calls smp_mb and not mb() I couldn't figure out why - original patches did mb() there. Outside core kernel - drm_cache_flush_clflush, drm_clflush_sg, drm_clflush_virt_range. Then there's gru_start_instruction in drivers/misc/sgi-gru/. But otherwise drivers/misc/sgi-gru/ calls clflush in gru_flush_cache without calling mb() - this could be a bug. Looking at all users, it seems that only mwait_idle calls smp_mb, around clflush, others call mb(). So at least as a first step, maybe it makes sense to scope this down somewhat by changing mwait_idle to call mb() and then optimizing __smp_mb instead...

On Tue, Jan 12, 2016 at 02:25:24PM -0800, H. Peter Anvin wrote: > On 01/12/16 14:10, Michael S. Tsirkin wrote: > > mb() typically uses mfence on modern x86, but a micro-benchmark shows that it's > > 2 to 3 times slower than lock; addl $0,(%%e/rsp) that we use on older CPUs. > > > > So let's use the locked variant everywhere - helps keep the code simple as >

On Tue, Jan 12, 2016 at 02:25:24PM -0800, H. Peter Anvin wrote: > On 01/12/16 14:10, Michael S. Tsirkin wrote: > > mb() typically uses mfence on modern x86, but a micro-benchmark shows that it's > > 2 to 3 times slower than lock; addl $0,(%%e/rsp) that we use on older CPUs. > > > > So let's use the locked variant everywhere - helps keep the code simple as >