lkml.org 
[lkml]   [2017]   [Sep]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: [PATCH 4/4][RFC v2] x86/apic: Spread the vectors by choosing the idlest CPU
On Wed, 6 Sep 2017, Yu Chen wrote:
> On Wed, Sep 06, 2017 at 12:57:41AM +0200, Thomas Gleixner wrote:
> > I have a hard time to figure out how the 133 vectors on CPU31 are now
> > magically fitting in the empty space on CPU0, which is 204 - 133 = 71. In
> > my limited understanding of math 133 is greater than 71, but your patch
> > might make that magically be wrong.
> >
> The problem is reproduced when the network cable is not plugged in,
> because this driver looks like this:
>
> step 1. Reserved enough irq vectors and corresponding IRQs.
> step 2. If the network is activated, invoke request_irq() to
> register the handler.
> step 3. Invoke set_affinity() to spread the IRQs onto different
> CPUs, thus to spread the vectors too.
>
> Here's my understanding for why spreading vectors might help for this
> special case:
> As step 2 will not get invoked, the IRQs of this driver
> has not been enabled, thus in migrate_one_irq() this IRQ
> will not be considered because there is a check of
> irqd_is_started(d), thus there should only be 8 vectors
> allocated by this driver on CPU0, and 8 vectors left on
> CPU31, and the 8 vectors on CPU31 will not be migrated
> to CPU0 neither, so there is room for other 'valid' vectors
> to be migrated to CPU0.

Can you please spare me repeating your theories, as long as you don't have
hard facts to back them up? The network cable is changing the symptoms,
but the underlying root cause is definitely something different.

> # cat /sys/kernel/debug/irq/domains/*
> name: VECTOR
> size: 0
> mapped: 388
> flags: 0x00000041

So we have 388 vectors mapped in total. And those are just device vectors
because system vectors are not accounted there.

> name: IO-APIC-0
> size: 24
> mapped: 16

That's the legacy space

> name: IO-APIC-1
> size: 8
> mapped: 2

> name: IO-APIC-2
> size: 8
> mapped: 0

> name: IO-APIC-3
> size: 8
> mapped: 0

> name: IO-APIC-4
> size: 8
> mapped: 5

And a few GSIs: Total GSIs = 16 + 2 + 5 = 23

> name: PCI-MSI-2
> size: 0
> mapped: 365

Plus 365 PCI-MSI vectors allocated.

> flags: 0x00000051
> parent: VECTOR
> name: VECTOR
> size: 0
> mapped: 388

Which nicely sums up to 388

> # ls /sys/kernel/debug/irq/irqs
> ls /sys/kernel/debug/irq/irqs
> 0 10 11 13 142 184 217 259 292 31 33 337 339
> 340 342 344 346 348 350 352 354 356 358 360 362
> 364 366 368 370 372 374 376 378 380 382 384 386
> 388 390 392 394 4 6 7 9 1 109 12 14 15 2
> 24 26 3 32 335 338 34 341 343 345 347 349
> 351 353 355 357 359 361 363 365 367 369 371 373
> 375 377 379 381 383 385 387 389 391 393 395 5
> 67 8

That are all interrupts which are active. That's a total of 89. Can you
explain where the delta of 299 vectors comes from?

299 allocated, vector mapped, but unused interrupts?

That's where your problem is, not in the vector spreading. You have a
massive leak.

> BTW, do we have sysfs to display how much vectors used on each CPUs?

Not yet.

Can you please apply the debug patch below, boot the machine and right
after login provide the output of

# cat /sys/kernel/debug/tracing/trace

Thanks,

tglx

8<-------------------
--- a/kernel/irq/msi.c
+++ b/kernel/irq/msi.c
@@ -372,6 +372,9 @@ int msi_domain_alloc_irqs(struct irq_dom
return ret;
}

+ trace_printk("dev: %s nvec %d virq %d\n",
+ dev_name(dev), desc->nvec_used, virq);
+
for (i = 0; i < desc->nvec_used; i++)
irq_set_msi_desc_off(virq, i, desc);
}
@@ -419,6 +422,8 @@ void msi_domain_free_irqs(struct irq_dom
* entry. If that's the case, don't do anything.
*/
if (desc->irq) {
+ trace_printk("dev: %s nvec %d virq %d\n",
+ dev_name(dev), desc->nvec_used, desc->irq);
irq_domain_free_irqs(desc->irq, desc->nvec_used);
desc->irq = 0;
}
\
 
 \ /
  Last update: 2017-09-06 10:04    [W:0.056 / U:6.620 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site