Netdev List

* Re: [PKT_SCHED]: PSCHED_TADD() and PSCHED_TADD2() can result,tv_usec >= 1000000
From: Shuya MAEDA @ 2006-06-21  0:16 UTC (permalink / raw)
  To: David Miller; +Cc: netdev
In-Reply-To: <20060619.235105.82052619.davem@davemloft.net>

Thank you for the comment.
I made the patch that used the loop instead of the divide and modulus.
Are there any comments?

David Miller wrote:
> From: Shuya MAEDA <maeda-sxb@necst.nec.co.jp>
> Date: Mon, 19 Jun 2006 14:36:46 +0900
> 
>>  #define PSCHED_TADD2(tv, delta, tv_res) \
>>  ({ \
>> -          int __delta = (tv).tv_usec + (delta); \
>> -          (tv_res).tv_sec = (tv).tv_sec; \
>> -          if (__delta > USEC_PER_SEC) { (tv_res).tv_sec++; __delta -= USEC_PER_SEC; } \
>> -          (tv_res).tv_usec = __delta; \
>> +          int __delta = (delta); \
>> +          (tv_res) = (tv); \
>> +          if((delta) > USEC_PER_SEC) { \
>> +                (tv_res).tv_sec += (delta) / USEC_PER_SEC; \
>> +                __delta -= (delta) % USEC_PER_SEC; \
>> +          } \
>> +          (tv_res).tv_usec += __delta; \
>> +          if((tv_res).tv_usec >= USEC_PER_SEC) { \
>> +                (tv_res).tv_sec++; \
>> +                (tv_res).tv_usec -= USEC_PER_SEC; \
>> +          } \
>>  })
> 
> Divide and modulus can be extremely expensive on some systems, so
> let's try to avoid using them.
> 
> It is probably sufficient to adjust the passed in delta only once if
> it is >= USEC_PER_SEC, but if you feel that is an unsafe assumption
> then please use a simply loop like this:
> 
> 	while (__delta >= USEC_PER_SEC) {
> 		(tv_res).tv_sec++;
> 		__delta -= USEC_PER_SEC;
> 	}
> 
> And please provide a proper "Signed-off-by: " line in your next
> patch submission.
> 
> Thank you very much.

Signed-off-by: Shuya MAEDA <maeda-sxb@necst.nec.co.jp>

diff -Nur linux-2.6.17.orig/include/net/pkt_sched.h linux-2.6.17.mypatch/include/net/pkt_sched.h

--- linux-2.6.17.orig/include/net/pkt_sched.h   2006-06-18 10:49:35.000000000 +0900
+++ linux-2.6.17.mypatch/include/net/pkt_sched.h        2006-06-20 17:17:34.000000000 +0900
@@ -169,17 +169,23 @@

  #define PSCHED_TADD2(tv, delta, tv_res) \
  ({ \
-          int __delta = (tv).tv_usec + (delta); \
-          (tv_res).tv_sec = (tv).tv_sec; \
-          if (__delta > USEC_PER_SEC) { (tv_res).tv_sec++; __delta -= USEC_PER_SEC; } \
+          int __delta = (delta); \
+          (tv_res) = (tv); \
+          while(__delta >= USEC_PER_SEC){ \
+                (tv_res).tv_sec++; \
+                __delta -= USEC_PER_SEC; \
+          } \
            (tv_res).tv_usec = __delta; \
  })

  #define PSCHED_TADD(tv, delta) \
  ({ \
-          (tv).tv_usec += (delta); \
-          if ((tv).tv_usec > USEC_PER_SEC) { (tv).tv_sec++; \
-                (tv).tv_usec -= USEC_PER_SEC; } \
+          int __delta = (delta); \
+          while(__delta >= USEC_PER_SEC){ \
+                (tv).tv_sec++; \
+                __delta -= USEC_PER_SEC; \
+          } \
+          (tv).tv_usec = __delta; \
  })

  /* Set/check that time is in the "past perfect";

-- 
Shuya MAEDA

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