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SubjectRe: [PATCH V2] tipc: Use bsearch library function
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On 09/16/2017 05:26 PM, Joe Perches wrote:
> On Sat, 2017-09-16 at 17:02 +0800, Ying Xue wrote:
>> On 09/16/2017 03:50 PM, Thomas Meyer wrote:
>>> Use common library function rather than explicitly coding
>>> some variant of it yourself.
>>>
>>> Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
>>
>> Acked-by: Ying Xue <ying.xue@windriver.com>
>
> Are you sure you want to do this?
>
> Note the comment above nameseq_find_subseq
>
> * Very time-critical, so binary searches through sub-sequence array.
>
> What impact does this change have on performance?

Sorry, I couldn't see any essential difference between this new
implementation and the original one except that the former tries to use
the library function - bsearch() to replace the original binary search
algorithm implemented in TIPC itself. Therefore, I don't think the
change will have a big impact on performance.

If I miss something, please let me know.

Thanks,
Ying

>
>>> diff --git a/net/tipc/name_table.c b/net/tipc/name_table.c
>>> index bd0aac87b41a..eeb4d7a13de2 100644
>>> --- a/net/tipc/name_table.c
>>> +++ b/net/tipc/name_table.c
>>> @@ -44,6 +44,7 @@
>>> #include "addr.h"
>>> #include "node.h"
>>> #include <net/genetlink.h>
>>> +#include <linux/bsearch.h>
>>>
>>> #define TIPC_NAMETBL_SIZE 1024 /* must be a power of 2 */
>>>
>>> @@ -168,6 +169,18 @@ static struct name_seq *tipc_nameseq_create(u32 type, struct hlist_head *seq_hea
>>> return nseq;
>>> }
>>>
>>> +static int nameseq_find_subseq_cmp(const void *key, const void *elt)
>>> +{
>>> + struct sub_seq *sseq = (struct sub_seq *)elt;
>>> + u32 instance = *(u32 *)key;
>>> +
>>> + if (instance < sseq->lower)
>>> + return -1;
>>> + else if (instance > sseq->upper)
>>> + return 1;
>>> + return 0;
>>> +}
>>> +
>>> /**
>>> * nameseq_find_subseq - find sub-sequence (if any) matching a name instance
>>> *
>>> @@ -176,21 +189,8 @@ static struct name_seq *tipc_nameseq_create(u32 type, struct hlist_head *seq_hea
>>> static struct sub_seq *nameseq_find_subseq(struct name_seq *nseq,
>>> u32 instance)
>>> {
>>> - struct sub_seq *sseqs = nseq->sseqs;
>>> - int low = 0;
>>> - int high = nseq->first_free - 1;
>>> - int mid;
>>> -
>>> - while (low <= high) {
>>> - mid = (low + high) / 2;
>>> - if (instance < sseqs[mid].lower)
>>> - high = mid - 1;
>>> - else if (instance > sseqs[mid].upper)
>>> - low = mid + 1;
>>> - else
>>> - return &sseqs[mid];
>>> - }
>>> - return NULL;
>>> + return bsearch(&instance, nseq->sseqs, nseq->first_free,
>>> + sizeof(struct sub_seq), nameseq_find_subseq_cmp);
>>> }
>>>
>>> /**
>>>
>

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