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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