Messages in this thread | | | Date | Wed, 16 Jul 2014 02:05:20 +0200 | Subject | Re: [PATCH v2 1/5] perf: add ability to sample machine state on interrupt | From | Stephane Eranian <> |
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On Tue, Jul 15, 2014 at 4:16 PM, Peter Zijlstra <peterz@infradead.org> wrote: > On Tue, Jul 15, 2014 at 02:31:40AM +0200, Stephane Eranian wrote: >> @@ -595,7 +595,8 @@ struct perf_sample_data { >> struct perf_callchain_entry *callchain; >> struct perf_raw_record *raw; >> struct perf_branch_stack *br_stack; >> - struct perf_regs_user regs_user; >> + struct perf_regs regs_user; >> + struct perf_regs regs_intr; >> u64 stack_user_size; >> u64 weight; >> /* >> @@ -618,6 +619,8 @@ static inline void perf_sample_data_init(struct perf_sample_data *data, >> data->weight = 0; >> data->data_src.val = 0; >> data->txn = 0; >> + data->regs_intr.abi = PERF_SAMPLE_REGS_ABI_NONE; >> + data->regs_intr.regs = NULL; >> } > > I don't think we've been very careful here; does the below make sense? > > AFAICT we don't need to set stack_user_size at all, > perf_prepare_sample() will set it when required, and with the change to > perf_sample_regs_user() the same is true for the regs_user thing. > > This again reduces the cost of perf_sample_data_init() to touching a > single cacheline. > > I'm not entirely sure the ____cacheline_aligned makes sense though, the > previous stack line is probably touched already so any next cacheline is > the one, and one avg we'd gain 0.5 cachelines worth of data. > > I am okay with the changes in this patch.
> > --- > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h > index 707617a8c0f6..d27fec8118b1 100644 > --- a/include/linux/perf_event.h > +++ b/include/linux/perf_event.h > @@ -575,34 +575,40 @@ extern u64 perf_event_read_value(struct perf_event *event, > > > struct perf_sample_data { > - u64 type; > + /* > + * Fields set by perf_sample_data_init(), group so as to > + * minimize the cachelines touched. > + */ > + u64 addr; > + struct perf_raw_record *raw; > + struct perf_branch_stack *br_stack; > + u64 period; > + u64 weight; > + u64 txn; > + union perf_mem_data_src data_src; > + > > + /* > + * The other fields, optionally {set,used} by > + * perf_{prepare,output}_sample(). > + */ > + u64 type; > u64 ip; > struct { > u32 pid; > u32 tid; > } tid_entry; > u64 time; > - u64 addr; > u64 id; > u64 stream_id; > struct { > u32 cpu; > u32 reserved; > } cpu_entry; > - u64 period; > - union perf_mem_data_src data_src; > struct perf_callchain_entry *callchain; > - struct perf_raw_record *raw; > - struct perf_branch_stack *br_stack; > struct perf_regs_user regs_user; > u64 stack_user_size; > - u64 weight; > - /* > - * Transaction flags for abort events: > - */ > - u64 txn; > -}; > +} ____cacheline_aligned; > > static inline void perf_sample_data_init(struct perf_sample_data *data, > u64 addr, u64 period) > @@ -612,9 +618,6 @@ static inline void perf_sample_data_init(struct perf_sample_data *data, > data->raw = NULL; > data->br_stack = NULL; > data->period = period; > - data->regs_user.abi = PERF_SAMPLE_REGS_ABI_NONE; > - data->regs_user.regs = NULL; > - data->stack_user_size = 0; > data->weight = 0; > data->data_src.val = 0; > data->txn = 0; > diff --git a/kernel/events/core.c b/kernel/events/core.c > index c8b53c94d41d..926cd7aafc14 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -4299,6 +4299,8 @@ perf_output_sample_regs(struct perf_output_handle *handle, > static void perf_sample_regs_user(struct perf_regs_user *regs_user, > struct pt_regs *regs) > { > + regs_user->abi = PERF_SAMPLE_REGS_ABI_NONE; > + > if (!user_mode(regs)) { > if (current->mm) > regs = task_pt_regs(current);
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