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Subject: RE: [PATCH 1/1] selftest/net: fix FILE_SIZE for 32 bit
 architecture.
Reply-To: maninder1.s@samsung.com
From:   Maninder Singh <maninder1.s@samsung.com>
To:     Eric Dumazet <eric.dumazet@gmail.com>,
        "davem@davemloft.net" <davem@davemloft.net>,
        "shuahkh@osg.samsung.com" <shuahkh@osg.samsung.com>
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        PANKAJ MISHRA <pankaj.m@samsung.com>,
        AMIT SAHRAWAT <a.sahrawat@samsung.com>,
        Vaneet Narang <v.narang@samsung.com>
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Date:   Fri, 03 Aug 2018 09:01:59 +0530
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Hi,

>On 08/02/2018 03:31 AM, Maninder Singh wrote:
>> FILE_SZ is defined as (1UL << 35), it will overflow
>> for 32 bit system and logic will break.
>> 
>> Signed-off-by: Maninder Singh <maninder1.s@samsung.com>
>> Signed-off-by: Vaneet Narang <v.narang@samsung.com>
>> ---
>>  tools/testing/selftests/net/tcp_mmap.c | 8 ++++----
>>  1 file changed, 4 insertions(+), 4 deletions(-)
>> 
>> diff --git a/tools/testing/selftests/net/tcp_mmap.c b/tools/testing/selftests/net/tcp_mmap.c
>> index e8c5dff..1d6ca12 100644
>> --- a/tools/testing/selftests/net/tcp_mmap.c
>> +++ b/tools/testing/selftests/net/tcp_mmap.c
>> @@ -85,7 +85,7 @@
>>  #define MSG_ZEROCOPY    0x4000000
>>  #endif
>>  
>> -#define FILE_SZ (1UL << 35)
>> +#define FILE_SZ (1ULL << 35)

...
...
>> @@ -431,7 +431,7 @@ int main(int argc, char *argv[])
>>                  zflg = 0;
>>          }
>>          while (total < FILE_SZ) {
>> -                long wr = FILE_SZ - total;
>> +                unsigned long long wr = FILE_SZ - total;
>>  
>>                  if (wr > chunk_size)
>>                          wr = chunk_size;
>> 
> 
>What about using more conventional size_t instead of "unsigned long long" ?

size_t is also equivalent to unsigned long and it will not hold value of (1 << 35) for 32 bit system.
So we can do two things.

(1) reduce FILE SIZE to (1 << 30), so that UL (size_t) can hold this value.
It will not show any perofrmance boost with ZEROCOPY. (checked on x86_64)

(2) use unsigned long long to work with both 32 and 64 bit system.
It will show performance boost with ZEROCOPY.(checked on x86_64)

What do you think?

Thanks and regards,
Maninder Singh