From 79ab11cdb90d8536817ab7357ecb6b1ff76be26c Mon Sep 17 00:00:00 2001 From: Christian Borntraeger Date: Tue, 25 Oct 2016 11:03:11 +0200 Subject: locking/core: Introduce cpu_relax_yield() For spinning loops people do often use barrier() or cpu_relax(). For most architectures cpu_relax and barrier are the same, but on some architectures cpu_relax can add some latency. For example on power,sparc64 and arc, cpu_relax can shift the CPU towards other hardware threads in an SMT environment. On s390 cpu_relax does even more, it uses an hypercall to the hypervisor to give up the timeslice. In contrast to the SMT yielding this can result in larger latencies. In some places this latency is unwanted, so another variant "cpu_relax_lowlatency" was introduced. Before this is used in more and more places, lets revert the logic and provide a cpu_relax_yield that can be called in places where yielding is more important than latency. By default this is the same as cpu_relax on all architectures. Signed-off-by: Christian Borntraeger Signed-off-by: Peter Zijlstra (Intel) Cc: Catalin Marinas Cc: Heiko Carstens Cc: Linus Torvalds Cc: Martin Schwidefsky Cc: Nicholas Piggin Cc: Noam Camus Cc: Peter Zijlstra Cc: Russell King Cc: Thomas Gleixner Cc: Will Deacon Cc: linuxppc-dev@lists.ozlabs.org Cc: virtualization@lists.linux-foundation.org Cc: xen-devel@lists.xenproject.org Link: http://lkml.kernel.org/r/1477386195-32736-2-git-send-email-borntraeger@de.ibm.com Signed-off-by: Ingo Molnar --- arch/s390/kernel/processor.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'arch/s390/kernel') diff --git a/arch/s390/kernel/processor.c b/arch/s390/kernel/processor.c index 81d0808085e6..9e60ef144d03 100644 --- a/arch/s390/kernel/processor.c +++ b/arch/s390/kernel/processor.c @@ -53,7 +53,7 @@ void s390_update_cpu_mhz(void) on_each_cpu(update_cpu_mhz, NULL, 0); } -void notrace cpu_relax(void) +void notrace cpu_relax_yield(void) { if (!smp_cpu_mtid && MACHINE_HAS_DIAG44) { diag_stat_inc(DIAG_STAT_X044); @@ -61,7 +61,7 @@ void notrace cpu_relax(void) } barrier(); } -EXPORT_SYMBOL(cpu_relax); +EXPORT_SYMBOL(cpu_relax_yield); /* * cpu_init - initializes state that is per-CPU. -- cgit From 760928c0dafc7d0faf0c0248e28e16d4c8dc7ad6 Mon Sep 17 00:00:00 2001 From: Christian Borntraeger Date: Wed, 2 Nov 2016 05:08:32 -0400 Subject: locking/spinlocks, s390: Implement vcpu_is_preempted(cpu) This implements the s390 version for vcpu_is_preempted(cpu), by reworking the existing smp_vcpu_scheduled() function into arch_vcpu_is_preempted(). We can then also get rid of the local cpu_is_preempted() function by moving the CIF_ENABLED_WAIT test into arch_vcpu_is_preempted(). Signed-off-by: Christian Borntraeger Signed-off-by: Peter Zijlstra (Intel) Acked-by: Heiko Carstens Cc: David.Laight@ACULAB.COM Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: benh@kernel.crashing.org Cc: boqun.feng@gmail.com Cc: bsingharora@gmail.com Cc: dave@stgolabs.net Cc: jgross@suse.com Cc: kernellwp@gmail.com Cc: konrad.wilk@oracle.com Cc: linuxppc-dev@lists.ozlabs.org Cc: mpe@ellerman.id.au Cc: paulmck@linux.vnet.ibm.com Cc: paulus@samba.org Cc: pbonzini@redhat.com Cc: rkrcmar@redhat.com Cc: virtualization@lists.linux-foundation.org Cc: will.deacon@arm.com Cc: xen-devel-request@lists.xenproject.org Cc: xen-devel@lists.xenproject.org Link: http://lkml.kernel.org/r/1478077718-37424-6-git-send-email-xinhui.pan@linux.vnet.ibm.com Signed-off-by: Ingo Molnar --- arch/s390/kernel/smp.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) (limited to 'arch/s390/kernel') diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c index 35531fe1c5ea..b988ed1d75ad 100644 --- a/arch/s390/kernel/smp.c +++ b/arch/s390/kernel/smp.c @@ -368,10 +368,15 @@ int smp_find_processor_id(u16 address) return -1; } -int smp_vcpu_scheduled(int cpu) +bool arch_vcpu_is_preempted(int cpu) { - return pcpu_running(pcpu_devices + cpu); + if (test_cpu_flag_of(CIF_ENABLED_WAIT, cpu)) + return false; + if (pcpu_running(pcpu_devices + cpu)) + return false; + return true; } +EXPORT_SYMBOL(arch_vcpu_is_preempted); void smp_yield_cpu(int cpu) { -- cgit