| Message ID | 1576277282-6590-2-git-send-email-igor.druzhinin@citrix.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | vTSC performance improvements | expand |
On Fri, Dec 13, 2019 at 10:48:01PM +0000, Igor Druzhinin wrote: > They either need to be transformed to atomics to work correctly > (currently they left unprotected for HVM domains) or dropped entirely ^ are used > as taking a per-domain spinlock is too expensive for high-vCPU count > domains even for debug build given this lock is taken too often. > > Choose the latter as they are not extremely important anyway. > > Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com> I don't find those counters specially useful TBH, but I'm not sure whether others find them useful. The change LGTM, so: Reviewed-by: Roger Pau Monné <roger.pau@citrix.com> Thanks, Roger.
On 16/12/2019 09:47, Roger Pau Monné wrote: > On Fri, Dec 13, 2019 at 10:48:01PM +0000, Igor Druzhinin wrote: >> They either need to be transformed to atomics to work correctly >> (currently they left unprotected for HVM domains) or dropped entirely > ^ are used >> as taking a per-domain spinlock is too expensive for high-vCPU count >> domains even for debug build given this lock is taken too often. >> >> Choose the latter as they are not extremely important anyway. >> >> Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com> > I don't find those counters specially useful TBH, but I'm not sure whether > others find them useful. The change LGTM, so: > > Reviewed-by: Roger Pau Monné <roger.pau@citrix.com> Jan and I already considered dropping them once (because of the HVM observation), but didn't find any harm with keeping them, seeing as they were diagnostic-only. I suspect they were put in for PVRDTSCP which has since been dropped. We now have a clear case where dropping them is of use to Xen. Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c index 47573f7..614ed60 100644 --- a/xen/arch/x86/hvm/hvm.c +++ b/xen/arch/x86/hvm/hvm.c @@ -3405,37 +3405,9 @@ int hvm_vmexit_cpuid(struct cpu_user_regs *regs, unsigned int inst_len) return hvm_monitor_cpuid(inst_len, leaf, subleaf); } -static uint64_t _hvm_rdtsc_intercept(void) -{ - struct vcpu *curr = current; -#if !defined(NDEBUG) || defined(CONFIG_PERF_COUNTERS) - struct domain *currd = curr->domain; - - if ( currd->arch.vtsc ) - switch ( hvm_guest_x86_mode(curr) ) - { - case 8: - case 4: - case 2: - if ( unlikely(hvm_get_cpl(curr)) ) - { - case 1: - currd->arch.vtsc_usercount++; - break; - } - /* fall through */ - case 0: - currd->arch.vtsc_kerncount++; - break; - } -#endif - - return hvm_get_guest_tsc(curr); -} - void hvm_rdtsc_intercept(struct cpu_user_regs *regs) { - msr_split(regs, _hvm_rdtsc_intercept()); + msr_split(regs, hvm_get_guest_tsc(current)); HVMTRACE_2D(RDTSC, regs->eax, regs->edx); } @@ -3464,7 +3436,7 @@ int hvm_msr_read_intercept(unsigned int msr, uint64_t *msr_content) break; case MSR_IA32_TSC: - *msr_content = _hvm_rdtsc_intercept(); + *msr_content = hvm_get_guest_tsc(v); break; case MSR_IA32_TSC_ADJUST: diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c index 27a3a10..216169a 100644 --- a/xen/arch/x86/time.c +++ b/xen/arch/x86/time.c @@ -2135,13 +2135,6 @@ uint64_t pv_soft_rdtsc(const struct vcpu *v, const struct cpu_user_regs *regs) spin_lock(&d->arch.vtsc_lock); -#if !defined(NDEBUG) || defined(CONFIG_PERF_COUNTERS) - if ( guest_kernel_mode(v, regs) ) - d->arch.vtsc_kerncount++; - else - d->arch.vtsc_usercount++; -#endif - if ( (int64_t)(now - d->arch.vtsc_last) > 0 ) d->arch.vtsc_last = now; else @@ -2318,11 +2311,6 @@ static void dump_softtsc(unsigned char key) printk(",khz=%"PRIu32, d->arch.tsc_khz); if ( d->arch.incarnation ) printk(",inc=%"PRIu32, d->arch.incarnation); -#if !defined(NDEBUG) || defined(CONFIG_PERF_COUNTERS) - if ( d->arch.vtsc_kerncount | d->arch.vtsc_usercount ) - printk(",vtsc count: %"PRIu64" kernel,%"PRIu64" user", - d->arch.vtsc_kerncount, d->arch.vtsc_usercount); -#endif printk("\n"); domcnt++; } diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h index 212303f..3780287 100644 --- a/xen/include/asm-x86/domain.h +++ b/xen/include/asm-x86/domain.h @@ -374,10 +374,6 @@ struct arch_domain hardware TSC scaling cases */ uint32_t incarnation; /* incremented every restore or live migrate (possibly other cases in the future */ -#if !defined(NDEBUG) || defined(CONFIG_PERF_COUNTERS) - uint64_t vtsc_kerncount; - uint64_t vtsc_usercount; -#endif /* Pseudophysical e820 map (XENMEM_memory_map). */ spinlock_t e820_lock;
They either need to be transformed to atomics to work correctly (currently they left unprotected for HVM domains) or dropped entirely as taking a per-domain spinlock is too expensive for high-vCPU count domains even for debug build given this lock is taken too often. Choose the latter as they are not extremely important anyway. Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com> --- xen/arch/x86/hvm/hvm.c | 32 ++------------------------------ xen/arch/x86/time.c | 12 ------------ xen/include/asm-x86/domain.h | 4 ---- 3 files changed, 2 insertions(+), 46 deletions(-)