Messages in this thread | | | Date | Mon, 15 Dec 2008 17:09:27 -0700 | From | "Dan Williams" <> | Subject | Re: [PATCH 11/13] dmaengine: kill struct dma_client and supporting infrastructure |
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On Fri, Dec 12, 2008 at 7:29 AM, Sosnowski, Maciej <maciej.sosnowski@intel.com> wrote: > Williams, Dan J wrote: >> All users have been converted to either the general-purpose allocator, >> dma_find_channel, or dma_request_channel. >> >> Signed-off-by: Dan Williams <dan.j.williams@intel.com> >> --- > (...) >> /** >> - * dma_chans_notify_available - broadcast available channels to the >> clients >> - */ >> -static void dma_clients_notify_available(void) >> -{ >> - struct dma_client *client; >> - >> - mutex_lock(&dma_list_mutex); >> - >> - list_for_each_entry(client, &dma_client_list, global_node) >> - dma_client_chan_alloc(client); >> - >> - mutex_unlock(&dma_list_mutex); >> -} > > I agree with Guennadi's concern about removing clients' notification > of new devices available in the system. > I understand that this design is based on polling instead, > however polling is always less efficient approach. > Do you think that restoring notifications in this redesigned dmaengine > would be more painful than limiting clients to polling solution? >
You are missing that net_dma has always "polled". Consider the case of how net_dma currently operates prior to ioatdma.ko being loaded. It periodically calls get_softnet_dma() to see if a channel is available, if it does not find one it falls back to a cpu copy. All that has changed is replacing this custom channel allocation routine with the unified dma_find_channel() interface. Channel notifications are not required. Either everything is built-in to guarantee that an engine is available upon request[1], or the client is smart enough to run without a channel for while like net_dma and raid offload.
Regards, Dan
[1] http://marc.info/?l=linux-kernel&m=122835195303213&w=2
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