mbuf autotuning effect

[Warner Losh]

On Sep 6, 2013, at 7:11 PM, Adrian Chadd wrote:

> Yeah, why is VM_KMEM_SIZE only 12mbyte for MIPS? That's a little low for a
> platform that has a direct map that's slightly larger than 12mb :)
> 
> Warner? Juli?

All architectures have it at 12MB, except sparc64 where it is 16MB. This can be changed with the options VM_KMEM_SIZE=xxxxx in the config file.

So my guess as to why this is the case: cut and paste worked, so nobody changed it after that.

# Still need to reads hiren's email to comprehend it...

Warner


> 
> 
> -adrian
> 
> 
> 
> On 6 September 2013 16:36, hiren panchasara <hiren.panchasara at gmail.com>wrote:
> 
>> We are seeing an interesting thing on a mips board with 32MB ram.
>> 
>> We run out of mbuf very easily and looking at numbers it seems we are only
>> getting 6mb of maxmbufmem.
>> 
>> # sysctl -a | grep hw | grep mem
>> hw.physmem: 33554432
>> hw.usermem: 21774336
>> hw.realmem: 33554432
>> #
>> # sysctl -a | grep maxmbuf
>> kern.ipc.maxmbufmem: 6291456
>> 
>> I believe that number is very low for a board with 32mb of ram.
>> 
>> Looking at the code:
>> 
>> sys/kern/kern_mbuf.c : tunable_mbinit()
>> 
>> 124         realmem = qmin((quad_t)physmem * PAGE_SIZE, vm_kmem_size);
>> 125         maxmbufmem = realmem / 2;
>> 126         TUNABLE_QUAD_FETCH("kern.ipc.maxmbufmem", &maxmbufmem);
>> 127         if (maxmbufmem > realmem / 4 * 3)
>> 128                 maxmbufmem = realmem / 4 * 3;
>> 
>> So, realmem plays important role in determining maxmbufmem.
>> 
>> physmem = 32mb
>> PAGE_SIZE = 4096
>> 
>> vm_kmem_size is calculated inside sys/kern/kern_malloc.c : kmeminit()
>> 
>> 705         vm_kmem_size = VM_KMEM_SIZE + nmbclusters * PAGE_SIZE;
>> 706         mem_size = cnt.v_page_count;
>> 707
>> 708 #if defined(VM_KMEM_SIZE_SCALE)
>> 709         vm_kmem_size_scale = VM_KMEM_SIZE_SCALE;
>> 710 #endif
>> 711         TUNABLE_INT_FETCH("vm.kmem_size_scale", &vm_kmem_size_scale);
>> 712         if (vm_kmem_size_scale > 0 &&
>> 713             (mem_size / vm_kmem_size_scale) > (vm_kmem_size /
>> PAGE_SIZE))
>> 714                 vm_kmem_size = (mem_size / vm_kmem_size_scale) *
>> PAGE_SIZE;
>> 
>> here,
>> VM_KMEM_SIZE = 12*1024*1024
>> nmbclusters = 0 (initially)
>> PAGE_SIZE = 4096
>> # sysctl -a | grep v_page_count
>> vm.stats.vm.v_page_count: 7035
>> 
>> and VM_KMEM_SIZE_SCALE = 3 for mips.
>> 
>> So, vm_kmem_size = 12mb.
>> 
>> Going back to tunable_mbinit(),
>> we get realmem = 12mb.
>> and masmbufmem = 6mb.
>> 
>> 
>> Wanted to see if I am following the code correctly and how autotuning
>> should work here.
>> 
>> cheers,
>> Hiren
>> _______________________________________________
>> freebsd-net at freebsd.org mailing list
>> http://lists.freebsd.org/mailman/listinfo/freebsd-net
>> To unsubscribe, send any mail to "freebsd-net-unsubscribe at freebsd.org"
>> 
> _______________________________________________
> freebsd-mips at freebsd.org mailing list
> http://lists.freebsd.org/mailman/listinfo/freebsd-mips
> To unsubscribe, send any mail to "freebsd-mips-unsubscribe at freebsd.org"