On Sat, Feb 02, 2008 at 11:31:31AM +0200, Alexander Motin wrote: >To check UMA dependency I have made a trivial one-element cache which in my >test case allows to avoid two for four allocations per packet.
You should be able to implement this lockless using atomic(9). I haven't
verified it, but the following should work.
>.....alloc.....
>- item = uma_zalloc(ng_qzone, wait | M_ZERO);
>+ mtx_lock_spin(&itemcachemtx);
>+ item = itemcache;
>+ itemcache = NULL;
>+ mtx_unlock_spin(&itemcachemtx);
= item = atomic_readandclear_ptr(&itemcache);
>+ if (item == NULL)
>+ item = uma_zalloc(ng_qzone, wait | M_ZERO);
>+ else
>+ bzero(item, sizeof(*item));
>.....free.....
>- uma_zfree(ng_qzone, item);
>+ mtx_lock_spin(&itemcachemtx);
>+ if (itemcache == NULL) {
>+ itemcache = item;
>+ item = NULL;
>+ }
>+ mtx_unlock_spin(&itemcachemtx);
>+ if (item)
>+ uma_zfree(ng_qzone, item);
= if (atomic_cmpset_ptr(&itemcache, NULL, item) == 0)
= uma_zfree(ng_qzone, item);
--
Peter Jeremy
Please excuse any delays as the result of my ISP's inability to implement
an MTA that is either RFC2821-compliant or matches their claimed behaviour.
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