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Message-ID: <20140715141625.GH9918@twins.programming.kicks-ass.net>
Date: Tue, 15 Jul 2014 16:16:25 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Stephane Eranian <eranian@...gle.com>
Cc: linux-kernel@...r.kernel.org, mingo@...e.hu, ak@...ux.intel.com,
jolsa@...hat.com, acme@...hat.com, namhyung@...nel.org
Subject: Re: [PATCH v2 1/5] perf: add ability to sample machine state on
interrupt
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.
---
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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