lkml.org 
[lkml]   [2011]   [Feb]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: IGMP and rwlock: Dead ocurred again on TILEPro
From
On Fri, Feb 18, 2011 at 7:18 AM, Chris Metcalf <cmetcalf@tilera.com> wrote:
> On 2/17/2011 6:11 PM, David Miller wrote:
>> From: Chris Metcalf <cmetcalf@tilera.com>
>> Date: Thu, 17 Feb 2011 18:04:13 -0500
>>
>>> On 2/17/2011 5:53 PM, David Miller wrote:
>>>> From: Chris Metcalf <cmetcalf@tilera.com>
>>>> Date: Thu, 17 Feb 2011 17:49:46 -0500
>>>>
>>>>> The fix is to disable interrupts for the arch_read_lock family of methods.
>>>> How does that help handle the race when it happens between different
>>>> cpus, instead of between IRQ and non-IRQ context on the same CPU?
>>> There's no race in that case, since the lock code properly backs off and
>>> retries until the other cpu frees it. The distinction here is that the
>>> non-IRQ context is "wedged" by the IRQ context.
>>>
>>>> Why don't you just use the generic spinlock based rwlock code on Tile,
>>>> since that is all that your atomic instructions can handle
>>>> sufficiently?
>>> The tile-specific code encodes reader/writer information in the same 32-bit
>>> word that the test-and-set instruction manipulates, so it's more efficient
>>> both in space and time. This may not really matter for rwlocks, since no
>>> one cares much about them any more, but that was the motivation.
>> Ok, but IRQ disabling is going to be very expensive.
>
> The interrupt architecture on Tile allows a write to a special-purpose
> register to put you into a "critical section" where no interrupts or faults
> are delivered. So we just need to bracket the read_lock operations with
> two SPR writes; each takes six machine cycles, so we're only adding 12
> cycles to the total cost of taking or releasing a read lock on an rwlock.
>
> --
> Chris Metcalf, Tilera Corp.
> http://www.tilera.com
>
>

Adding that to SPR writes should be fine, but it may cause interrupt
delay a little more that other platform's read_lock()?

Another question: What NMI in the former mail means?

Looking forward to your patch.

Regards

--
Cyberman Wu


\
 
 \ /
  Last update: 2011-02-18 08:11    [from the cache]
©2003-2011 Jasper Spaans