Date: Thu, 08 Dec 2011 12:49:18 -0500 From: John Baldwin <jhb@FreeBSD.org> To: Luigi Rizzo <rizzo@iet.unipi.it> Cc: svn-src-head@freebsd.org, Luigi Rizzo <luigi@freebsd.org>, src-committers@freebsd.org, svn-src-all@freebsd.org, Marius Strobl <marius@alchemy.franken.de> Subject: Re: svn commit: r228281 - in head/sys/dev: e1000 re Message-ID: <4EE0F89E.1070107@FreeBSD.org> In-Reply-To: <20111205193150.GB49118@onelab2.iet.unipi.it> References: <201112051533.pB5FXEuh043063@svn.freebsd.org> <20111205183854.GC54475@alchemy.franken.de> <20111205193150.GB49118@onelab2.iet.unipi.it>
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On 12/5/11 2:31 PM, Luigi Rizzo wrote:
> On Mon, Dec 05, 2011 at 07:38:54PM +0100, Marius Strobl wrote:
>> On Mon, Dec 05, 2011 at 03:33:14PM +0000, Luigi Rizzo wrote:
> ...
>>> +#ifdef DEV_NETMAP
>>> + if (slot) {
>>> + int si = i + na->tx_rings[txr->me].nkr_hwofs;
>>> + void *addr;
>>> +
>>> + if (si>= na->num_tx_desc)
>>> + si -= na->num_tx_desc;
>>> + addr = NMB(slot + si);
>>> + txr->tx_base[i].buffer_addr =
>>> + htole64(vtophys(addr));
>>> + /* reload the map for netmap mode */
>>> + netmap_load_map(txr->txtag,
>>> + txbuf->map, addr, na->buff_size);
>>> + }
>>> +#endif /* DEV_NETMAP */
>>
>> Can these vtophys(9) usages be fixed to use bus_dma(9) instead so netmap
>> works with bounce buffers, IOMMUs etc?
>
> maybe. Can you suggest how to change it ?
>
> Consider that (not here but in other places) vtophys() is called
> in a time-critical loop so performance matters a lot. As long as i
> can compute the physical address in advance and cache it in my own
> array, i suppose that should be fine (in which case the calls to
> vtophys(addr) would become NMPB(slot + si) where the NMPB() macro
> would hide translations and checks.
For your use case, you probably don't want to be coping with bounce
buffers at all. That is, if you are preallocating long-lived buffers
that keep getting reused while netmap is active that are allocated at
startup and free'd at teardown, you probably want to allocate buffers
that won't require bounce buffers. That means you have to let the
drivers allocate the buffers (or give you a suitable bus_dma tag since
different devices have different addressing requirements, etc.). You
could then use bus_dmamem_alloc() to allocate your buffers.
--
John Baldwin
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