Re[2]: 3.5G user space speed

Peter Zaitsev
2002-01-15T21:27:30Z

Hello Brian,

Wednesday, January 16, 2002, 12:05:39 AM, you wrote:

Well. May be you can tell about the numbers a bit ? I can chose 3.0G
for user instead of 3.5G for user with not really huge loss, but I'd
like to know how much it will increase speed and in which cases, also
about standard 2/2 mode.

>>
>> 2.4.xaa Series as well as SuSE kernels have 3.5G userspace option,
>> which seems to be quite useful, therefore I see it's not included
>> is stock kernel for some reasons. Also I've heard this
>> configuration may have some performance problems.
>>
>> Can anyone comment on this topic ?
>>
>> I need large amount of address space for my application but I also
>> need to get as much I/O performance as it's possible, so I can switch
>> to 3.0/1.0 memory distribution if it will benefit here.

BG> You can't have it both ways with the x86 (speed vs. large userspace).
BG> Kernel 2.5 may help a bit here because changes were made to allow DMA
BG> from all memory (subject to card limitations), lessening the burden for
BG> direct-mapped memory. Otherwise you'll need to move to a 64-bit arch.