On Sat, Mar 19, 2016 at 1:35 PM, Torsten Bögershausen <tboegi@xxxxxx> wrote:
> On 2016-03-19 02.19, David Turner wrote:
>> Each write() has syscall overhead, and writing a large index entails
>> many such calls. A larger write buffer reduces the overhead,
>> leading to increased performance.
>>
>> On my repo, which has an index size of 30m, this saves about 10ms of
>> time writing the index.
>>
>> Signed-off-by: David Turner <dturner@xxxxxxxxxxxxxxxx>
>> ---
>> read-cache.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/read-cache.c b/read-cache.c
>> index d9fb78b..09ebe08 100644
>> --- a/read-cache.c
>> +++ b/read-cache.c
>> @@ -1714,7 +1714,7 @@ int unmerged_index(const struct index_state *istate)
>> return 0;
>> }
>>
>> -#define WRITE_BUFFER_SIZE 8192
>> +#define WRITE_BUFFER_SIZE 131072
>> static unsigned char write_buffer[WRITE_BUFFER_SIZE];
>> static unsigned long write_buffer_len;
>>
>>
> Do I read that right, it saves 10 milliseconds ?
> What happens to small system (like Raspberry PI), when you
> want 128K write buffer ?
> Could the buffer size be turned into a makefile variable, defaulting to 8192 ?
Maybe for all ARM devices not just Raspberry Pi.
There is one way, though its not that good. This is just a sample
code. I am unsure about if using bash in makefile is a good idea
in Makefile,
uname -a | grep "arm" >out
if [ -s out ]; then
export ARM=arm
fi
rm out
in read-cache.c,
#define ARCH (getenv("ARCH"))
#ifdef ARCH,
#define WRITE_BUFFER_SIZE 128000
#endif
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