Messages in this thread | | | Date | Mon, 23 Dec 2019 17:52:57 +0100 | From | Jesper Dangaard Brouer <> | Subject | Re: [net-next v5 PATCH] page_pool: handle page recycle for NUMA_NO_NODE condition |
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On Mon, 23 Dec 2019 09:57:00 +0200 Ilias Apalodimas <ilias.apalodimas@linaro.org> wrote:
> Hi Jesper, > > Looking at the overall path again, i still need we need to reconsider > pool->p.nid semantics. > > As i said i like the patch and the whole functionality and code seems fine, > but here's the current situation.
> If a user sets pool->p.nid == NUMA_NO_NODE and wants to use > page_pool_update_nid() the whole behavior feels a liitle odd.
As soon as driver uses page_pool_update_nid() than means they want to control the NUMA placement explicitly. As soon as that happens, it is the drivers responsibility and choice, and page_pool API must respect that (and not automatically change that behind drivers back).
> page_pool_update_nid() first check will always be true since .nid = > NUMA_NO_NODE). Then we'll update this to a real nid. So we end up > overwriting what the user initially coded in. > > This is close to what i proposed in the previous mails on this > thread. Always store a real nid even if the user explicitly requests > NUMA_NO_NODE. > > So semantics is still a problem. I'll stick to what we initially > suggested. > 1. We either *always* store a real nid > or > 2. If NUMA_NO_NODE is present ignore every other check and recycle > the memory blindly. >
Hmm... I actually disagree with both 1 and 2.
My semantics proposal: If driver configures page_pool with NUMA_NO_NODE, then page_pool tried to help get the best default performance. (Which according to performance measurements is to have RX-pages belong to the NUMA node RX-processing runs on).
The reason I want this behavior is that during driver init/boot, it can easily happen that a driver allocates RX-pages from wrong NUMA node. This will cause a performance slowdown, that normally doesn't happen, because without a cache (like page_pool) RX-pages would fairly quickly transition over to the RX NUMA node (instead we keep recycling these, in your case #2, where you suggest recycle blindly in case of NUMA_NO_NODE). IMHO page_pool should hide this border-line case from driver developers.
--Jesper
> On Fri, Dec 20, 2019 at 06:06:49PM +0200, Ilias Apalodimas wrote: > > On Fri, Dec 20, 2019 at 04:22:54PM +0100, Jesper Dangaard Brouer > > wrote: > > > On Fri, 20 Dec 2019 12:49:37 +0200 > > > Ilias Apalodimas <ilias.apalodimas@linaro.org> wrote: > > > > > > > On Fri, Dec 20, 2019 at 11:41:16AM +0100, Jesper Dangaard > > > > Brouer wrote: > > > > > On Fri, 20 Dec 2019 12:23:14 +0200 > > > > > Ilias Apalodimas <ilias.apalodimas@linaro.org> wrote: > > > > > > > > > > > Hi Jesper, > > > > > > > > > > > > I like the overall approach since this moves the check out > > > > > > of the hotpath. @Saeed, since i got no hardware to test > > > > > > this on, would it be possible to check that it still works > > > > > > fine for mlx5? > > > > > > > > > > > > [...] > > > > > > > + struct ptr_ring *r = &pool->ring; > > > > > > > + struct page *page; > > > > > > > + int pref_nid; /* preferred NUMA node */ > > > > > > > + > > > > > > > + /* Quicker fallback, avoid locks when ring is > > > > > > > empty */ > > > > > > > + if (__ptr_ring_empty(r)) > > > > > > > + return NULL; > > > > > > > + > > > > > > > + /* Softirq guarantee CPU and thus NUMA node is > > > > > > > stable. This, > > > > > > > + * assumes CPU refilling driver RX-ring will > > > > > > > also run RX-NAPI. > > > > > > > + */ > > > > > > > + pref_nid = (pool->p.nid == NUMA_NO_NODE) ? > > > > > > > numa_mem_id() : pool->p.nid; > > > > > > > > > > > > One of the use cases for this is that during the allocation > > > > > > we are not guaranteed to pick up the correct NUMA node. > > > > > > This will get automatically fixed once the driver starts > > > > > > recycling packets. > > > > > > > > > > > > I don't feel strongly about this, since i don't usually > > > > > > like hiding value changes from the user but, would it make > > > > > > sense to move this into __page_pool_alloc_pages_slow() and > > > > > > change the pool->p.nid? > > > > > > > > > > > > Since alloc_pages_node() will replace NUMA_NO_NODE with > > > > > > numa_mem_id() regardless, why not store the actual node in > > > > > > our page pool information? You can then skip this and check > > > > > > pool->p.nid == numa_mem_id(), regardless of what's > > > > > > configured. > > > > > > > > > > This single code line helps support that drivers can control > > > > > the nid themselves. This is a feature that is only used my > > > > > mlx5 AFAIK. > > > > > > > > > > I do think that is useful to allow the driver to "control" > > > > > the nid, as pinning/preferring the pages to come from the > > > > > NUMA node that matches the PCI-e controller hardware is > > > > > installed in does have benefits. > > > > > > > > Sure you can keep the if statement as-is, it won't break > > > > anything. Would we want to store the actual numa id in > > > > pool->p.nid if the user selects 'NUMA_NO_NODE'? > > > > > > No. pool->p.nid should stay as NUMA_NO_NODE, because that makes it > > > dynamic. If someone moves an RX IRQ to another CPU on another > > > NUMA node, then this 'NUMA_NO_NODE' setting makes pages > > > transitioned automatically. > > Ok this assumed that drivers were going to use > > page_pool_nid_changed(), but with the current code we don't have to > > force them to do that. Let's keep this as-is. > > > > I'll be running a few more tests and wait in case Saeed gets a > > chance to test it and send my reviewed-by
-- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
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