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SubjectRe: [PATCH 2/2] perf sort: Improve symbol sort output by separating unresolved samples by type
 On Wed, 31 Aug 2011 11:51:45 +1000, Anton Blanchard wrote:
> I took a profile that suggested 60% of total CPU time was in the
> hypervisor:
>
> # perf report --sort symbol
> ...
> 60.20% [H] 0x33d43c
> 4.43% [k] ._spin_lock_irqsave
> 1.07% [k] ._spin_lock
>
> Using perf stat to get the user/kernel/hypervisor breakdown
> contradicted
> this.
>
> The problem is we merge all unresolved samples into the one unknown
> bucket. If add a comparison by sample type to sort__sym_cmp we get
> the
> real picture:
>
> # perf report --sort symbol
> ...
> 57.11% [.] 0x80fbf63c
> 4.43% [k] ._spin_lock_irqsave
> 1.07% [k] ._spin_lock
> 0.65% [H] 0x33d43c
>
> So it was almost all userspace, not hypervisor as the initial profile
> suggested.
>
> I found another issue while adding this. Symbol sorting sometimes
> shows
> multiple entries for the unknown bucket:
>
> # perf report --sort symbol
> ...
> 16.65% [.] 0x6cd3a8
> 7.25% [.] 0x422460
> 5.37% [.] yylex
> 4.79% [.] malloc
> 4.78% [.] _int_malloc
> 4.03% [.] _int_free
> 3.95% [.] hash_source_code_string
> 2.82% [.] 0x532908
> 2.64% [.] 0x36b538
> 0.94% [H] 0x8000000000e132a4
> 0.82% [H] 0x800000000000e8b0
>
> This happens because we aren't consistent with our sorting. On
> one hand we check to see if both symbols match and for two unresolved
> samples sym is NULL so we match:
>
> if (left->ms.sym == right->ms.sym)
> return 0;
>
> On the other hand we use sample IP for unresolved samples when
> comparing against a symbol:
>
> ip_l = left->ms.sym ? left->ms.sym->start : left->ip;
> ip_r = right->ms.sym ? right->ms.sym->start : right->ip;
>
> This means unresolved samples end up spread across the rbtree and we
> can't merge them all.
>
> If we use cmp_null all unresolved samples will end up in the one
> bucket
> and the output makes more sense:
>
> # perf report --sort symbol
> ...
> 39.12% [.] 0x36b538
> 5.37% [.] yylex
> 4.79% [.] malloc
> 4.78% [.] _int_malloc
> 4.03% [.] _int_free
> 3.95% [.] hash_source_code_string
> 2.26% [H] 0x800000000000e8b0
>
> Signed-off-by: Anton Blanchard <anton@samba.org>


Acked-by: Eric B Munson <emunson@mgebm.net>



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