Re: [RFC PATCH v3 7/7] x86/unwind/orc: remove run-time ORC unwind tables sort

Shile Zhang
2019-11-18T10:50:28Z

On 2019/11/18 18:05, David Laight wrote:
> From: Josh Poimboeuf <jpoimboe@redhat.com>
>> Sent: 15 November 2019 17:47
>> On Fri, Nov 15, 2019 at 04:51:24PM +0000, David Laight wrote:
>>> From: Shile Zhang
>>>> Sent: 15 November 2019 06:48
>>> ...
>>>> arch/x86/kernel/unwind_orc.c | 8 +++++---
>>>> 1 file changed, 5 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
>>>> index 332ae6530fa8..280da6fa9922 100644
>>>> --- a/arch/x86/kernel/unwind_orc.c
>>>> +++ b/arch/x86/kernel/unwind_orc.c
>>>> @@ -273,9 +273,11 @@ void __init unwind_init(void)
>>>> return;
>>>> }
>>>>
>>>> - /* Sort the .orc_unwind and .orc_unwind_ip tables: */
>>>> - sort(__start_orc_unwind_ip, num_entries, sizeof(int), orc_sort_cmp,
>>>> - orc_sort_swap);
>>>> + /*
>>>> + * Note, orc_unwind and orc_unwind_ip tables has been sorted in
>>>> + * vmlinux link phase by sorttable tool at build time.
>>>> + * Its ready for binary search now.
>>>> + */
>>> How fast is sort() if the table is sorted?
>>> Relying on the kernel sources and build scripts always being in sync seems dangerous.
>>> Probably better to leave the sort in for a release of two.
>> This patch comes after the build script changes, so they'd be in sync.
>> What would the concern be?
> Mostly that if, for any reason, the build script changes are missing nothing
> will detect the error - but the results will be very confusing.
> If the sort is fast for sorted inputs (some algorithms aren't) then leaving
> it in won't take that long.
>
> David

Hi, David,

Thanks for your review!
Due to the sort inside kernel is heap-sort, so it cost almost the same
time for sorted inputs.
I wondered if we can add error handling in the link script, exit with
error if sort encountered any errors.

Thanks!

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