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SubjectRe: [PATCH V4 08/10] powerpc, perf: Enable SW filtering in branch stack sampling framework
On 12/10/2013 11:27 AM, Anshuman Khandual wrote:
> On 12/09/2013 11:51 AM, Michael Ellerman wrote:
>> This code was already in need of some unindentation, and now it's just
>> ridiculous.
>>
>> To start with at the beginning of this routine we have:
>>
>> while (..) {
>> if (!val)
>> break;
>> else {
>> // Bulk of the logic
>> ...
>> }
>> }
>>
>> That should almost always become:
>>
>> while (..) {
>> if (!val)
>> break;
>>
>> // Bulk of the logic
>> ...
>> }
>>
>>
>> But in this case that's not enough. Please send a precursor patch which moves
>> this logic out into a helper function.
>
> Hey Michael,
>
> I believe this patch should be able to take care of this.
>
> commit d66d729715cabe0cfd8e34861a6afa8ad639ddf3
> Author: Anshuman Khandual <khandual@linux.vnet.ibm.com>
> Date: Tue Dec 10 11:10:06 2013 +0530
>
> power, perf: Clean up BHRB processing
>
> This patch cleans up some indentation problem and re-organizes the
> BHRB processing code with an additional helper function.
>
> Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
>
> diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
> index 29b89e8..9ae96c5 100644
> --- a/arch/powerpc/perf/core-book3s.c
> +++ b/arch/powerpc/perf/core-book3s.c
> @@ -400,11 +400,20 @@ static __u64 power_pmu_bhrb_to(u64 addr)
> return target - (unsigned long)&instr + addr;
> }
>
> +void update_branch_entry(struct cpu_hw_events *cpuhw, int u_index, u64 from, u64 to, int pred)
> +{
> + cpuhw->bhrb_entries[u_index].from = from;
> + cpuhw->bhrb_entries[u_index].to = to;
> + cpuhw->bhrb_entries[u_index].mispred = pred;
> + cpuhw->bhrb_entries[u_index].predicted = ~pred;
> + return;
> +}
> +
> /* Processing BHRB entries */
> void power_pmu_bhrb_read(struct cpu_hw_events *cpuhw)
> {
> u64 val;
> - u64 addr;
> + u64 addr, tmp;
> int r_index, u_index, pred;
>
> r_index = 0;
> @@ -415,62 +424,54 @@ void power_pmu_bhrb_read(struct cpu_hw_events *cpuhw)
> if (!val)
> /* Terminal marker: End of valid BHRB entries */
> break;
> - else {
> - addr = val & BHRB_EA;
> - pred = val & BHRB_PREDICTION;
>
> - if (!addr)
> - /* invalid entry */
> - continue;
> + addr = val & BHRB_EA;
> + pred = val & BHRB_PREDICTION;
>
> - /* Branches are read most recent first (ie. mfbhrb 0 is
> - * the most recent branch).
> - * There are two types of valid entries:
> - * 1) a target entry which is the to address of a
> - * computed goto like a blr,bctr,btar. The next
> - * entry read from the bhrb will be branch
> - * corresponding to this target (ie. the actual
> - * blr/bctr/btar instruction).
> - * 2) a from address which is an actual branch. If a
> - * target entry proceeds this, then this is the
> - * matching branch for that target. If this is not
> - * following a target entry, then this is a branch
> - * where the target is given as an immediate field
> - * in the instruction (ie. an i or b form branch).
> - * In this case we need to read the instruction from
> - * memory to determine the target/to address.
> + if (!addr)
> + /* invalid entry */
> + continue;
> +
> + /* Branches are read most recent first (ie. mfbhrb 0 is
> + * the most recent branch).
> + * There are two types of valid entries:
> + * 1) a target entry which is the to address of a
> + * computed goto like a blr,bctr,btar. The next
> + * entry read from the bhrb will be branch
> + * corresponding to this target (ie. the actual
> + * blr/bctr/btar instruction).
> + * 2) a from address which is an actual branch. If a
> + * target entry proceeds this, then this is the
> + * matching branch for that target. If this is not
> + * following a target entry, then this is a branch
> + * where the target is given as an immediate field
> + * in the instruction (ie. an i or b form branch).
> + * In this case we need to read the instruction from
> + * memory to determine the target/to address.
> + */
> + if (val & BHRB_TARGET) {
> + /* Target branches use two entries
> + * (ie. computed gotos/XL form)
> */
> + tmp = addr;
>
> + /* Get from address in next entry */
> + val = read_bhrb(r_index++);
> + addr = val & BHRB_EA;
> if (val & BHRB_TARGET) {
> - /* Target branches use two entries
> - * (ie. computed gotos/XL form)
> - */
> - cpuhw->bhrb_entries[u_index].to = addr;
> - cpuhw->bhrb_entries[u_index].mispred = pred;
> - cpuhw->bhrb_entries[u_index].predicted = ~pred;
> -
> - /* Get from address in next entry */
> - val = read_bhrb(r_index++);
> - addr = val & BHRB_EA;
> - if (val & BHRB_TARGET) {
> - /* Shouldn't have two targets in a
> - row.. Reset index and try again */
> - r_index--;
> - addr = 0;
> - }
> - cpuhw->bhrb_entries[u_index].from = addr;
> - } else {
> - /* Branches to immediate field
> - (ie I or B form) */
> - cpuhw->bhrb_entries[u_index].from = addr;
> - cpuhw->bhrb_entries[u_index].to =
> - power_pmu_bhrb_to(addr);
> - cpuhw->bhrb_entries[u_index].mispred = pred;
> - cpuhw->bhrb_entries[u_index].predicted = ~pred;
> + /* Shouldn't have two targets in a
> + row.. Reset index and try again */
> + r_index--;
> + addr = 0;
> }
> - u_index++;
> -
> + update_branch_entry(cpuhw, u_index, addr, tmp, pred);
> + } else {
> + /* Branches to immediate field
> + (ie I or B form) */
> + tmp = power_pmu_bhrb_to(addr);
> + update_branch_entry(cpuhw, u_index, addr, tmp, pred);
> }
> + u_index++;
> }
> cpuhw->bhrb_stack.nr = u_index;
> return;

Hey Michael,

Does the patch looks okay ? In which case will send it out separately. Do let
me know. Thank you.

Regards
Anshuman



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