Gigabit Performance 2.4.19-preX - Excessive locks, calls, waits

/usr/src/linux/net/core/skbuff.c

//int sysctl_hot_list_len = 128;
int sysctl_hot_list_len = 1024; // bump this value up

alloc_skb_frame with fixed 1514 + fragment list allocations, sysctl_hot_list_len = 1024.

Quoted 5 lines · Jeff V. Merkey

/usr/src/linux/net/core/skbuff.c

//int sysctl_hot_list_len = 128;
int sysctl_hot_list_len = 1024; // bump this value up

The plan was to actually to get rid of the skb hot list. It was just a stop gap solution to get CPU local smp allocation before Linux had cpu local slab caches. The slab cache has been fixed and runs cpu local now too, so there should be no need for it anymore as the slab cache does essentially the same thing as the private hot list cache (maintaining linked lists of objects and unlinking them quickly on allocation and linking them again on free, all in O(1))

Quoted 2 lines

alloc_skb_frame with fixed 1514 + fragment list allocations, sysctl_hot_list_len = 1024.

Something is bogus with your profile data. Increasing sysctl_hot_list_len never changes the frequency with which kmalloc/kfree are called. All it does is to produce less calls to kmem_cache_alloc() for the skb head, but the skb data portion is always allocated using kmalloc(). Your new profile doesn't show kmalloc so you changed something else.

-andi