Date: Sun, 3 Feb 2008 06:36:56 +1100 From: Peter Jeremy <peterjeremy@optushome.com.au> To: Alexander Motin <mav@freebsd.org> Cc: freebsd-hackers@freebsd.org, freebsd-performance@freebsd.org Subject: Re: Memory allocation performance Message-ID: <20080202193656.GR35170@server.vk2pj.dyndns.org> In-Reply-To: <47A43873.40801@FreeBSD.org> References: <47A25412.3010301@FreeBSD.org> <47A25A0D.2080508@elischer.org> <47A2C2A2.5040109@FreeBSD.org> <20080201185435.X88034@fledge.watson.org> <47A43873.40801@FreeBSD.org>
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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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