Date: Fri, 6 Sep 2013 16:36:09 -0700 From: hiren panchasara <hiren.panchasara@gmail.com> To: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org>, "freebsd-mips@freebsd.org" <freebsd-mips@freebsd.org> Subject: mbuf autotuning effect Message-ID: <CALCpEUHoAS2RRyO7JVOeSKWKiss9vZmN%2BxA1BDpwHDpkEYcjEA@mail.gmail.com>
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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
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