search for: read_hv_clock_tsc

...I only need to replace virt_rmb() barriers with plain rmb() to get 'lfence' in hv_read_tsc_page (PATCH 2)? As members of struct ms_hyperv_tsc_page are volatile we don't need READ_ONCE(), compilers are not allowed to merge accesses. The resulting code looks good to me: (gdb) disassemble read_hv_clock_tsc Dump of assembler code for function read_hv_clock_tsc: 0xffffffff8102ca60 <+0>: callq 0xffffffff816c7500 <__fentry__> 0xffffffff8102ca65 <+5>: mov 0xf67974(%rip),%rcx # 0xffffffff81f943e0 <tsc_pg> 0xffffffff8102ca6c <+12>: jmp 0xffffffff8102ca87...

...I only need to replace virt_rmb() barriers with plain rmb() to get 'lfence' in hv_read_tsc_page (PATCH 2)? As members of struct ms_hyperv_tsc_page are volatile we don't need READ_ONCE(), compilers are not allowed to merge accesses. The resulting code looks good to me: (gdb) disassemble read_hv_clock_tsc Dump of assembler code for function read_hv_clock_tsc: 0xffffffff8102ca60 <+0>: callq 0xffffffff816c7500 <__fentry__> 0xffffffff8102ca65 <+5>: mov 0xf67974(%rip),%rcx # 0xffffffff81f943e0 <tsc_pg> 0xffffffff8102ca6c <+12>: jmp 0xffffffff8102ca87...

...stly for worse. If MS does the same thing, they should document it. 3. You need rdtsc_ordered(). Plain RDTSC is not ordered wrt other memory access, and it can observably screw up as a result. Also, Linux tries to avoid volatile variables, so please use READ_ONCE(). > > (gdb) disassemble read_hv_clock_tsc > Dump of assembler code for function read_hv_clock_tsc: > 0xffffffff8102ca60 <+0>: callq 0xffffffff816c7500 <__fentry__> > 0xffffffff8102ca65 <+5>: mov 0xf67974(%rip),%rcx # 0xffffffff81f943e0 <tsc_pg> > 0xffffffff8102ca6c <+12>...

...gorithm is good for SMP case (as we can't prevent the code in vdso from migrating between CPUs) I'd like to send v2 with some modifications to keep the discussion going. Changes since v1: - Document the TSC page reading protocol [Thomas Gleixner]. - Separate the TSC page reading code from read_hv_clock_tsc() and put it to asm/mshyperv.h to use from both hv_init.c and vdso. - Add explicit barriers [Thomas Gleixner] Original description: Hyper-V TSC page clocksource is suitable for vDSO, however, the protocol defined by the hypervisor is different from VCLOCK_PVCLOCK. Implemented the required supp...

...gorithm is good for SMP case (as we can't prevent the code in vdso from migrating between CPUs) I'd like to send v2 with some modifications to keep the discussion going. Changes since v1: - Document the TSC page reading protocol [Thomas Gleixner]. - Separate the TSC page reading code from read_hv_clock_tsc() and put it to asm/mshyperv.h to use from both hv_init.c and vdso. - Add explicit barriers [Thomas Gleixner] Original description: Hyper-V TSC page clocksource is suitable for vDSO, however, the protocol defined by the hypervisor is different from VCLOCK_PVCLOCK. Implemented the required supp...

...x86/hyperv/hv_init.c +++ b/arch/x86/hyperv/hv_init.c @@ -27,10 +27,15 @@ #include <linux/clockchips.h> -#ifdef CONFIG_X86_64 +#ifdef CONFIG_HYPERV_TSCPAGE static struct ms_hyperv_tsc_page *tsc_pg; +struct ms_hyperv_tsc_page *hv_get_tsc_page(void) +{ + return tsc_pg; +} + static u64 read_hv_clock_tsc(struct clocksource *arg) { u64 current_tick; @@ -136,7 +141,7 @@ void hyperv_init(void) /* * Register Hyper-V specific clocksource. */ -#ifdef CONFIG_X86_64 +#ifdef CONFIG_HYPERV_TSCPAGE if (ms_hyperv.features & HV_X64_MSR_REFERENCE_TSC_AVAILABLE) { union hv_x64_msr_hypercall_co...

...tition (as HV_MSR_REFERENCE_TSC_AVAILABLE is set), why don't we use it? (I understand that with TSC scaling support in modern CPUs even migration is a no-issue and we can use raw TSC but this all seems to be independent from root/non-root partition question). > hv_read_reference_counter = read_hv_clock_tsc; > phys_addr = virt_to_phys(hv_get_tsc_page()); -- Vitaly

...ypersior, we're not creating new structures (so I don't understand how we could use struct seqcount which we don't have) but I may be misunderstanding something. BTW, I just occured to me that I should've probably put the TSC reading code to mshyperv.h and use it from both vDSO and read_hv_clock_tsc() -- what do you thing? [snip] -- Vitaly

...ypersior, we're not creating new structures (so I don't understand how we could use struct seqcount which we don't have) but I may be misunderstanding something. BTW, I just occured to me that I should've probably put the TSC reading code to mshyperv.h and use it from both vDSO and read_hv_clock_tsc() -- what do you thing? [snip] -- Vitaly

Hi, Hyper-V TSC page clocksource is suitable for vDSO, however, the protocol defined by the hypervisor is different from VCLOCK_PVCLOCK. Implemented the required support. Simple sysbench test shows the following results: Before: # time sysbench --test=memory --max-requests=500000 run ... real 1m22.618s user 0m50.193s sys 0m32.268s After: # time sysbench --test=memory

Hi, Hyper-V TSC page clocksource is suitable for vDSO, however, the protocol defined by the hypervisor is different from VCLOCK_PVCLOCK. Implemented the required support. Simple sysbench test shows the following results: Before: # time sysbench --test=memory --max-requests=500000 run ... real 1m22.618s user 0m50.193s sys 0m32.268s After: # time sysbench --test=memory

On Wed, 3 Oct 2018, Andy Lutomirski wrote: > > On Oct 3, 2018, at 5:01 AM, Vitaly Kuznetsov <vkuznets at redhat.com> wrote: > > Not all Hyper-V hosts support reenlightenment notifications (and, if I'm > > not mistaken, you need to enable nesting for the VM to get the feature - > > and most VMs don't have this) so I think we'll have to keep Hyper-V >

...++ 2 files changed, 54 insertions(+), 32 deletions(-) diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c index 6b64cae..63dd00e 100644 --- a/arch/x86/hyperv/hv_init.c +++ b/arch/x86/hyperv/hv_init.c @@ -38,39 +38,11 @@ struct ms_hyperv_tsc_page *hv_get_tsc_page(void) static u64 read_hv_clock_tsc(struct clocksource *arg) { - u64 current_tick; + u64 current_tick = hv_read_tsc_page(tsc_pg); + + if (current_tick == U64_MAX) + rdmsrl(HV_X64_MSR_TIME_REF_COUNT, current_tick); - if (tsc_pg->tsc_sequence != 0) { - /* - * Use the tsc page to compute the value. - */ - - while (1) { -...

.../x86/hyperv/hv_init.c +++ b/arch/x86/hyperv/hv_init.c @@ -27,10 +27,15 @@ #include <linux/clockchips.h> -#ifdef CONFIG_X86_64 +#ifdef CONFIG_HYPERV_TSCPAGE static struct ms_hyperv_tsc_page *tsc_pg; +struct ms_hyperv_tsc_page *hv_get_tsc_page(void) { + return tsc_pg; +} + static u64 read_hv_clock_tsc(struct clocksource *arg) { u64 current_tick; @@ -136,7 +141,7 @@ void hyperv_init(void) /* * Register Hyper-V specific clocksource. */ -#ifdef CONFIG_X86_64 +#ifdef CONFIG_HYPERV_TSCPAGE if (ms_hyperv.features & HV_X64_MSR_REFERENCE_TSC_AVAILABLE) { union hv_x64_msr_hypercall_co...

.../x86/hyperv/hv_init.c +++ b/arch/x86/hyperv/hv_init.c @@ -27,10 +27,15 @@ #include <linux/clockchips.h> -#ifdef CONFIG_X86_64 +#ifdef CONFIG_HYPERV_TSCPAGE static struct ms_hyperv_tsc_page *tsc_pg; +struct ms_hyperv_tsc_page *hv_get_tsc_page(void) { + return tsc_pg; +} + static u64 read_hv_clock_tsc(struct clocksource *arg) { u64 current_tick; @@ -136,7 +141,7 @@ void hyperv_init(void) /* * Register Hyper-V specific clocksource. */ -#ifdef CONFIG_X86_64 +#ifdef CONFIG_HYPERV_TSCPAGE if (ms_hyperv.features & HV_X64_MSR_REFERENCE_TSC_AVAILABLE) { union hv_x64_msr_hypercall_co...

Hi, merge window is about to close so I hope it's OK to make another try here. Changes since v2: - Add explicit READ_ONCE() to not rely on 'volatile' [Andy Lutomirski] - rdtsc() -> rdtsc_ordered() [Andy Lutomirski] - virt_rmb() -> smp_rmb() [Thomas Gleixner, Andy Lutomirski] Thomas, Andy, it seems the only blocker for the series was the ambiguity with TSC page read algorithm.

Hi, merge window is about to close so I hope it's OK to make another try here. Changes since v2: - Add explicit READ_ONCE() to not rely on 'volatile' [Andy Lutomirski] - rdtsc() -> rdtsc_ordered() [Andy Lutomirski] - virt_rmb() -> smp_rmb() [Thomas Gleixner, Andy Lutomirski] Thomas, Andy, it seems the only blocker for the series was the ambiguity with TSC page read algorithm.

On Thu, 9 Feb 2017, Vitaly Kuznetsov wrote: > +#ifdef CONFIG_HYPERV_TSCPAGE > +static notrace u64 vread_hvclock(int *mode) > +{ > + const struct ms_hyperv_tsc_page *tsc_pg = > + (const struct ms_hyperv_tsc_page *)&hvclock_page; > + u64 sequence, scale, offset, current_tick, cur_tsc; > + > + while (1) { > + sequence = READ_ONCE(tsc_pg->tsc_sequence); > + if

On Thu, 9 Feb 2017, Vitaly Kuznetsov wrote: > +#ifdef CONFIG_HYPERV_TSCPAGE > +static notrace u64 vread_hvclock(int *mode) > +{ > + const struct ms_hyperv_tsc_page *tsc_pg = > + (const struct ms_hyperv_tsc_page *)&hvclock_page; > + u64 sequence, scale, offset, current_tick, cur_tsc; > + > + while (1) { > + sequence = READ_ONCE(tsc_pg->tsc_sequence); > + if

Hi, Hyper-V TSC page clocksource is suitable for vDSO, however, the protocol defined by the hypervisor is different from VCLOCK_PVCLOCK. I implemented the required support re-using pvclock_page VVAR. Simple sysbench test shows the following results: Before: # time sysbench --test=memory --max-requests=500000 run ... real 1m22.618s user 0m50.193s sys 0m32.268s After: # time sysbench