Messages in this thread | | | Subject | Re: [PATCH 06/13] irq: add a helper spread an affinity mask for MSI/MSI-X vectors | From | "Guilherme G. Piccoli" <> | Date | Wed, 15 Jun 2016 10:09:33 -0300 |
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Thanks for the responses Bart and Christoph.
On 06/15/2016 07:10 AM, Christoph Hellwig wrote: > On Tue, Jun 14, 2016 at 06:54:22PM -0300, Guilherme G. Piccoli wrote: >> On 06/14/2016 04:58 PM, Christoph Hellwig wrote: >>> This is lifted from the blk-mq code and adopted to use the affinity mask >>> concept just intruced in the irq handling code. >> >> Very nice patch Christoph, thanks. There's a little typo above, on >> "intruced". > > fixed. > >> Another little typo above in "assining". > > fixed a swell. > >> I take this opportunity to ask you something, since I'm working in a >> related code in a specific driver > > Which driver? One of the points here is to get this sort of code out > of drivers and into common code..
A network driver, i40e. I'd be glad to implement/see some common code to raise the topology information I need, but I was implementing on i40e more as a test case/toy example heheh...
>> - sorry in advance if my question is >> silly or if I misunderstood your code. >> >> The function irq_create_affinity_mask() below deals with the case in which >> we have nr_vecs < num_online_cpus(); in this case, wouldn't be a good idea >> to trying distribute the vecs among cores? >> >> Example: if we have 128 online cpus, 8 per core (meaning 16 cores) and 64 >> vecs, I guess would be ideal to distribute 4 vecs _per core_, leaving 4 >> CPUs in each core without vecs. > > There have been some reports about the blk-mq IRQ distribution being > suboptimal, but no one sent patches so far. This patch just moves the > existing algorithm into the core code to be better bisectable. > > I think an algorithm that takes cores into account instead of just SMT > sibling would be very useful. So if you have a case where this helps > for you an incremental patch (or even one against the current blk-mq > code for now) would be appreciated.
...but now I'll focus on the common/general case! Thanks for the suggestion Christoph. I guess would be even better to have a generic function that retrieves an optimal mask, something like topology_get_optimal_mask(n, *cpumask), in which we get the best distribution of n CPUs among all cores and return such a mask - interesting case is when n < num_online_cpus. So, this function could be used inside your irq_create_affinity_mask() and maybe in other places it is needed.
I was planning to use topology_core_id() to retrieve the core of a CPU, if anybody has a better idea, I'd be glad to hear it.
Cheers,
Guilherme
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