svn commit: r309143 - head/sys/libkern

[Fabien Thomas]

> Le 25 nov. 2016 à 17:00, Mateusz Guzik <mjguzik at gmail.com> a écrit :
> 
> On Fri, Nov 25, 2016 at 01:49:33PM +0000, Fabien Thomas wrote:
>> Author: fabient
>> Date: Fri Nov 25 13:49:33 2016
>> New Revision: 309143
>> URL: https://svnweb.freebsd.org/changeset/base/309143
>> 
>> Log:
>>  In a dual processor system (2*6 cores) during IPSec throughput tests,
>>  we see a lot of contention on the arc4 lock, used to generate the IV
>>  of the ESP output packets.
>> 
>>  The idea of this patch is to split this mutex in order to reduce the
>>  contention on this lock.
>> 
>> +MALLOC_DEFINE(M_ARC4RANDOM, "arc4random", "arc4random structures");
>> 
>> -static u_int8_t arc4_randbyte(void);
>> +struct arc4_s {
>> +	u_int8_t i, j;
>> +	int numruns;
>> +	u_int8_t sbox[256];
>> +	time_t t_reseed;
>> +
>> +	struct mtx mtx;
>> +};
>> +
> 
> Why is the lock at the end? Right now you got false sharing with the
> next entry.
> 
> That said, I suggest:
> 1. moving thelock to the beginning
> 2. annotating the struct with __aligned(CACHE_LINE_SIZE)

Yes good catch, it will be better that way. Committed as r309146.
Thanks

> 
> -- 
> Mateusz Guzik <mjguzik gmail.com>