On Mon, Jul 01, 2013 at 03:23:03PM +0800, Yan, Zheng wrote:
> From: "Yan, Zheng" <zheng.z....@intel.com>
>
> The x86 special perf event context is named x86_perf_event_context,
> We can enlarge it later to store PMU special data.
This changelog is completely inadequate. It fails to state what and why
we do things.
I hate doing this; but I can't see another way around it either. That
said:
> @@ -274,6 +274,11 @@ struct pmu {
> * flush branch stack on context-switches (needed in cpu-wide mode)
> */
> void (*flush_branch_stack) (void);
> +
> + /*
> + * Allocate PMU special perf event context
> + */
> + void *(*event_context_alloc) (struct perf_event_context *parent_ctx);
> };
It should be *optional*, also wtf is that parent_ctx thing for?
> +++ b/kernel/events/core.c
> @@ -2961,13 +2961,20 @@ static void __perf_event_init_context(struct
> perf_event_context *ctx)
> }
>
> static struct perf_event_context *
> -alloc_perf_context(struct pmu *pmu, struct task_struct *task)
> +alloc_perf_context(struct pmu *pmu, struct task_struct *task,
> + struct perf_event_context *parent_ctx)
> {
> struct perf_event_context *ctx;
>
> - ctx = kzalloc(sizeof(struct perf_event_context), GFP_KERNEL);
> - if (!ctx)
> - return NULL;
> + if (pmu->event_context_alloc) {
> + ctx = pmu->event_context_alloc(parent_ctx);
> + if (IS_ERR(ctx))
> + return ctx;
> + } else {
> + ctx = kzalloc(sizeof(struct perf_event_context), GFP_KERNEL);
> + if (!ctx)
> + return ERR_PTR(-ENOMEM);
> + }
>
> __perf_event_init_context(ctx);
> if (task) {
I'm not at all sure we want to do it like this; why not simply query the
size. Something like:
alloc_perf_context(struct pmu *pmu, struct task_struct *task)
{
size_t ctx_size = sizeof(struct perf_event_context);
if (pmu->task_context_size)
size = pmu->task_context_size();
ctx = kzalloc(size, GFP_KERNEL);
if (!ctx)
return ERR_PTR(-ENOMEM);
...
}
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