Re: [RFC 4/4] Restartable sequences: Add self-tests for PPC

[Boqun Feng <boqun.feng@gmail.com>]

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On Thu, Jul 28, 2016 at 02:59:45AM +0000, Mathieu Desnoyers wrote:
> ----- On Jul 27, 2016, at 11:05 AM, Boqun Feng boqun.feng@gmail.com wrote:
> 
> > As rseq syscall is enabled on PPC, implement the self-tests on PPC to
> > verify the implementation of the syscall.
> > 
> > Please note we only support 32bit userspace on BE kernel.
> > 
> > Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> > ---
> > tools/testing/selftests/rseq/param_test.c |  14 ++++
> > tools/testing/selftests/rseq/rseq.h       | 120 ++++++++++++++++++++++++++++++
> > 2 files changed, 134 insertions(+)
> > 
> > diff --git a/tools/testing/selftests/rseq/param_test.c
> > b/tools/testing/selftests/rseq/param_test.c
> > index db25e0a818e5..e2cb1b165f81 100644
> > --- a/tools/testing/selftests/rseq/param_test.c
> > +++ b/tools/testing/selftests/rseq/param_test.c
> > @@ -75,6 +75,20 @@ static __thread unsigned int yield_mod_cnt, nr_retry;
> > 	"bne 222b\n\t" \
> > 	"333:\n\t"
> > 
> > +#elif __PPC__
> > +#define INJECT_ASM_REG	"r18"
> > +
> > +#define RSEQ_INJECT_CLOBBER \
> > +	, INJECT_ASM_REG
> > +
> > +#define RSEQ_INJECT_ASM(n) \
> > +	"lwz %%" INJECT_ASM_REG ", %[loop_cnt_" #n "]\n\t" \
> > +	"cmpwi %%" INJECT_ASM_REG ", 0\n\t" \
> > +	"beq 333f\n\t" \
> > +	"222:\n\t" \
> > +	"subic. %%" INJECT_ASM_REG ", %%" INJECT_ASM_REG ", 1\n\t" \
> > +	"bne 222b\n\t" \
> > +	"333:\n\t"
> > #else
> > #error unsupported target
> > #endif
> > diff --git a/tools/testing/selftests/rseq/rseq.h
> > b/tools/testing/selftests/rseq/rseq.h
> > index 791e14cf42ae..dea0bea52566 100644
> > --- a/tools/testing/selftests/rseq/rseq.h
> > +++ b/tools/testing/selftests/rseq/rseq.h
> > @@ -138,6 +138,35 @@ do {									\
> > #define has_fast_acquire_release()	0
> > #define has_single_copy_load_64()	1
> > 
> > +#elif __PPC__
> > +#define smp_mb()	__asm__ __volatile__ ("sync" : : : "memory")
> > +#define smp_lwsync()	__asm__ __volatile__ ("lwsync" : : : "memory")
> > +#define smp_rmb()	smp_lwsync()
> > +#define smp_wmb()	smp_lwsync()
> > +
> > +#define smp_load_acquire(p)						\
> > +__extension__ ({							\
> > +	__typeof(*p) ____p1 = READ_ONCE(*p);				\
> > +	smp_lwsync();							\
> > +	____p1;								\
> > +})
> > +
> > +#define smp_acquire__after_ctrl_dep()	smp_lwsync()
> > +
> > +#define smp_store_release(p, v)						\
> > +do {									\
> > +	smp_lwsync();							\
> > +	WRITE_ONCE(*p, v);						\
> > +} while (0)
> > +
> > +#define has_fast_acquire_release()	1
> 
> Can you check if defining has_fast_acquire_release() to 0 speeds up
> performance significantly ? It turns the smp_lwsync() into a
> compiler barrier() on the smp_load_acquire() side (fast-path), and
> turn the smp_lwsync() into a membarrier system call instead of the
> matching smp_store_release() (slow path).
> 

Good point. Here are the numbers:

Power8 PSeries KVM Guest(64 VCPUs, the host has 16 cores, 128 hardware
threads):

                                 Counter increment speed (ns/increment)
                              1 thread   2 threads   4 threads   8 threads   16 threads   32 threads
global increment (baseline)     6.5          N/A         N/A         N/A       N/A           N/A
percpu rseq increment           7.0          7.0         7.2         7.2       9.3          14.5
percpu rseq spinlock           18.5         18.5        18.6        18.8      25.5          52.7

So looks like defining has_fast_acquire_release() to 0 could benefit the
cases with more threads in current benchmark. I will send a updated
patch doing this.

And as discussed in IRC, I will also remove jump from rseq_finish()
fast-path in powerpc asm in the updated patch as you did for x86 and
ARM.

Regards,
Boqun


> Thanks,
> 
> Mathieu
> 
> > +
> > +# if __PPC64__
> > +# define has_single_copy_load_64()	1
> > +# else
> > +# define has_single_copy_load_64()	0
> > +# endif
> > +
> > #else
> > #error unsupported target
> > #endif
> > @@ -404,6 +433,97 @@ bool rseq_finish(struct rseq_lock *rlock,
> > 			: succeed
> > 		);
> > 	}
> > +#elif __PPC64__
> > +	{
> > +		/*
> > +		 * The __rseq_table section can be used by debuggers to better
> > +		 * handle single-stepping through the restartable critical
> > +		 * sections.
> > +		 */
> > +		__asm__ __volatile__ goto (
> > +			".pushsection __rseq_table, \"aw\"\n\t"
> > +			".balign 8\n\t"
> > +			"4:\n\t"
> > +			".quad 1f, 2f, 3f\n\t"
> > +			".popsection\n\t"
> > +			"1:\n\t"
> > +			RSEQ_INJECT_ASM(1)
> > +			"lis %%r17, (4b)@highest\n\t"
> > +			"ori %%r17, %%r17, (4b)@higher\n\t"
> > +			"rldicr %%r17, %%r17, 32, 31\n\t"
> > +			"oris %%r17, %%r17, (4b)@h\n\t"
> > +			"ori %%r17, %%r17, (4b)@l\n\t"
> > +			"std %%r17, 0(%[rseq_cs])\n\t"
> > +			RSEQ_INJECT_ASM(2)
> > +			"lwz %%r17, %[current_event_counter]\n\t"
> > +			"li %%r16, 0\n\t"
> > +			"cmpw cr7, %[start_event_counter], %%r17\n\t"
> > +			"bne cr7, 3f\n\t"
> > +			RSEQ_INJECT_ASM(3)
> > +			"std %[to_write], 0(%[target])\n\t"
> > +			"2:\n\t"
> > +			RSEQ_INJECT_ASM(4)
> > +			"std %%r16, 0(%[rseq_cs])\n\t"
> > +			"b %l[succeed]\n\t"
> > +			"3:\n\t"
> > +			"li %%r16, 0\n\t"
> > +			"std %%r16, 0(%[rseq_cs])\n\t"
> > +			: /* no outputs */
> > +			: [start_event_counter]"r"(start_value.event_counter),
> > +			  [current_event_counter]"m"(start_value.rseqp->abi.u.e.event_counter),
> > +			  [to_write]"r"(to_write),
> > +			  [target]"b"(p),
> > +			  [rseq_cs]"b"(&start_value.rseqp->abi.rseq_cs)
> > +			  RSEQ_INJECT_INPUT
> > +			: "r16", "r17", "memory", "cc"
> > +			  RSEQ_INJECT_CLOBBER
> > +			: succeed
> > +		);
> > +	}
> > +#elif __PPC__
> > +	{
> > +		/*
> > +		 * The __rseq_table section can be used by debuggers to better
> > +		 * handle single-stepping through the restartable critical
> > +		 * sections.
> > +		 */
> > +		__asm__ __volatile__ goto (
> > +			".pushsection __rseq_table, \"aw\"\n\t"
> > +			".balign 8\n\t"
> > +			"4:\n\t"
> > +			".long 0x0, 1f, 0x0, 2f, 0x0, 3f\n\t" /* 32 bit only supported on BE */
> > +			".popsection\n\t"
> > +			"1:\n\t"
> > +			RSEQ_INJECT_ASM(1)
> > +			"lis %%r17, (4b)@ha\n\t"
> > +			"addi %%r17, %%r17, (4b)@l\n\t"
> > +			"stw %%r17, 0(%[rseq_cs])\n\t"
> > +			RSEQ_INJECT_ASM(2)
> > +			"lwz %%r17, %[current_event_counter]\n\t"
> > +			"li %%r16, 0\n\t"
> > +			"cmpw cr7, %[start_event_counter], %%r17\n\t"
> > +			"bne cr7, 3f\n\t"
> > +			RSEQ_INJECT_ASM(3)
> > +			"stw %[to_write], 0(%[target])\n\t"
> > +			"2:\n\t"
> > +			RSEQ_INJECT_ASM(4)
> > +			"stw %%r16, 0(%[rseq_cs])\n\t"
> > +			"b %l[succeed]\n\t"
> > +			"3:\n\t"
> > +			"li %%r16, 0\n\t"
> > +			"stw %%r16, 0(%[rseq_cs])\n\t"
> > +			: /* no outputs */
> > +			: [start_event_counter]"r"(start_value.event_counter),
> > +			  [current_event_counter]"m"(start_value.rseqp->abi.u.e.event_counter),
> > +			  [to_write]"r"(to_write),
> > +			  [target]"b"(p),
> > +			  [rseq_cs]"b"(&start_value.rseqp->abi.rseq_cs)
> > +			  RSEQ_INJECT_INPUT
> > +			: "r16", "r17", "memory", "cc"
> > +			  RSEQ_INJECT_CLOBBER
> > +			: succeed
> > +		);
> > +	}
> > #else
> > #error unsupported target
> > #endif
> > --
> > 2.9.0
> 
> -- 
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com

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