Messages in this thread | | | From | "Song Bao Hua (Barry Song)" <> | Subject | RE: [RFC PATCH 1/2] sched/topology: Get rid of NUMA overlapping groups | Date | Tue, 9 Feb 2021 00:12:30 +0000 |
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> -----Original Message----- > From: Valentin Schneider [mailto:valentin.schneider@arm.com] > Sent: Tuesday, February 9, 2021 12:48 AM > To: Song Bao Hua (Barry Song) <song.bao.hua@hisilicon.com>; > linux-kernel@vger.kernel.org > Cc: vincent.guittot@linaro.org; mgorman@suse.de; mingo@kernel.org; > peterz@infradead.org; dietmar.eggemann@arm.com; morten.rasmussen@arm.com; > linuxarm@openeuler.org; xuwei (O) <xuwei5@huawei.com>; Liguozhu (Kenneth) > <liguozhu@hisilicon.com>; tiantao (H) <tiantao6@hisilicon.com>; wanghuiqiang > <wanghuiqiang@huawei.com>; Zengtao (B) <prime.zeng@hisilicon.com>; Jonathan > Cameron <jonathan.cameron@huawei.com>; guodong.xu@linaro.org; Meelis Roos > <mroos@linux.ee> > Subject: RE: [RFC PATCH 1/2] sched/topology: Get rid of NUMA overlapping groups > > Hi Barry, > > On 08/02/21 10:04, Song Bao Hua (Barry Song) wrote: > >> -----Original Message----- > >> From: Valentin Schneider [mailto:valentin.schneider@arm.com] > > > > > Hi Valentin, > > > > While I like your approach, this will require more time > > to evaluate possible influence as the approach also affects > > all machines without 3-hops issue. So x86 platforms need to > > be tested and benchmark is required. > > > > What about we firstly finish the review of "grandchild" approach > > v2 and have a solution for kunpeng920 and Sun Fire X4600-M2 > > while not impacting other machines which haven't 3-hops issues > > first? > > > > I figured I'd toss this out while the iron was hot (and I had the topology > crud paged in), but I ultimately agree that it's better to first go with > something that fixes the diameter > 2 topologies and leaves the other ones > untouched, which is exactly what you have. > > > I would appreciate very much if you could comment on v2: > > > https://lore.kernel.org/lkml/20210203111201.20720-1-song.bao.hua@hisilicon > .com/ > > > > See my comment below on domain degeneration; with that taken care of I > would say it's good to go. Have a look at what patch1+patch3 squashed > together looks like, passing the right sd to init_overlap_sched_group() > looks a bit neater IMO. > > >> +static struct sched_domain *find_node_domain(struct sched_domain *sd) > >> +{ > >> + struct sched_domain *parent; > >> + > >> + BUG_ON(!(sd->flags & SD_NUMA)); > >> + > >> + /* Get to the level above NODE */ > >> + while (sd && sd->child) { > >> + parent = sd; > >> + sd = sd->child; > >> + > >> + if (!(sd->flags & SD_NUMA)) > >> + break; > >> + } > >> + /* > >> + * We're going to create cross topology level sched_group_capacity > >> + * references. This can only work if the domains resulting from said > >> + * levels won't be degenerated, as we need said sgc to be periodically > >> + * updated: it needs to be attached to the local group of a domain > >> + * that didn't get degenerated. > >> + * > >> + * Of course, groups aren't available yet, so we can't call the usual > >> + * sd_degenerate(). Checking domain spans is the closest we get. > >> + * Start from NODE's parent, and keep going up until we get a domain > >> + * we're sure won't be degenerated. > >> + */ > >> + while (sd->parent && > >> + cpumask_equal(sched_domain_span(sd), sched_domain_span(parent))) > { > >> + sd = parent; > >> + parent = sd->parent; > >> + } > > > > So this is because the sched_domain which doesn't contribute to scheduler > > will be destroyed during cpu_attach_domain() since sd and parent span > > the seam mask? > > > > Yes; let's take your topology for instance: > > node 0 1 2 3 > 0: 10 12 20 22 > 1: 12 10 22 24 > 2: 20 22 10 12 > 3: 22 24 12 10 > > 2 10 2 > 0 <---> 1 <---> 2 <---> 3
Guess you actually mean 2 10 2 1 <---> 0 <---> 2 <---> 3
> > > Domains for node1 will look like (before any fixes are applied): > > NUMA<=10: span=1 groups=(1) > NUMA<=12: span=0-1 groups=(1)->(0) > NUMA<=20: span=0-1 groups=(0,1) > NUMA<=22: span=0-2 groups=(0,1)->(0,2-3) > NUMA<=24: span=0-3 groups=(0-2)->(0,2-3) > > As you can see, the domain representing distance <= 20 will be degenerated > (it has a single group). If we were to e.g. add some more nodes to the left > of node0, then we would trigger the "grandchildren logic" for node1 and > would end up creating a reference to node1 NUMA<=20's sgc, which is a > mistake: that domain will be degenerated, and that sgc will never be > updated. The right thing to do here would be reference node1 NUMA<=12's > sgc, which the above snippet does.
Guess I got your point even though the diagram is not correct :-)
If the topology is as below(add a node left to node1 rather than node0):
9 2 10 2 A <---> 1 <---> 0 <---> 2 <---> 3
For nodeA, NUMA<=10: span=A groups=(A) NUMA<=12: span= A groups= (A) NUMA<=19: span=A-1 groups=(A),(1) NUMA<=20: span=A-1 groups=(A,1) *1 NUMA<=21: span=A-1-0 groups=(A,1), node1's numa<=20
For node0, NUMA<=10: span=9 groups=(0) #3 NUMA<=12: span=0-1 groups=(0)->(1) #2 NUMA<=19: span=0-1 groups=(0,1) #1 NUMA<=20: span=0-1-2 groups=(0,1),....
*1 will firstly try #1, and it finds 2 is outside the A-1-0, then it will try #2. Finally #2 will be degenerated, so we should actually use #3. Amazing!
> > >> + > >> + return parent; > >> +} > >> +
Thanks Barry
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