From: Waiman Long <waiman.long@hpe.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org, x86@kernel.org,
linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org,
linux-s390@vger.kernel.org, linux-arch@vger.kernel.org,
Davidlohr Bueso <dave@stgolabs.net>,
Jason Low <jason.low2@hp.com>, Dave Chinner <david@fromorbit.com>,
Scott J Norton <scott.norton@hpe.com>,
Douglas Hatch <doug.hatch@hpe.com>
Subject: Re: [RFC PATCH-tip v2 5/6] locking/rwsem: Change RWSEM_WAITING_BIAS for better disambiguation
Date: Wed, 15 Jun 2016 15:31:51 -0400 [thread overview]
Message-ID: <5761AD27.9020106@hpe.com> (raw)
In-Reply-To: <20160615174348.GT30921@twins.programming.kicks-ass.net>
On 06/15/2016 01:43 PM, Peter Zijlstra wrote:
> On Tue, Jun 14, 2016 at 06:48:08PM -0400, Waiman Long wrote:
>> even the reduced maximum of about 16k (32-bit) or 1G (64-bit) should
>> be more than enough for the foreseeable future.
> So what happens if I manage to create 16k+ threads on my 32bit kernel
> and get them all to do mmap() or so at the same time.
>
> That doesn't seem too far fetched.
>
> Then again, with double that (the current limit) that doesn't seem
> impossible either.
To hit the limit, we need to have all the threads calling down_write()
at exactly the same instance in time which, I think, is pretty hard to
do. Also, I don't believe you will ever see a 16k-cpu massive SMP system
running on 32-bit kernel. I can imagine such a system running on 64-bit
kernel, but certainly not 32-bit.
Cheers,
Longman
WARNING: multiple messages have this Message-ID (diff)
From: Waiman Long <waiman.long@hpe.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org, x86@kernel.org,
linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org,
linux-s390@vger.kernel.org, linux-arch@vger.kernel.org,
Davidlohr Bueso <dave@stgolabs.net>,
Jason Low <jason.low2@hp.com>, Dave Chinner <david@fromorbit.com>,
Scott J Norton <scott.norton@hpe.com>,
Douglas Hatch <doug.hatch@hpe.com>
Subject: Re: [RFC PATCH-tip v2 5/6] locking/rwsem: Change RWSEM_WAITING_BIAS for better disambiguation
Date: Wed, 15 Jun 2016 19:31:51 +0000 [thread overview]
Message-ID: <5761AD27.9020106@hpe.com> (raw)
In-Reply-To: <20160615174348.GT30921@twins.programming.kicks-ass.net>
On 06/15/2016 01:43 PM, Peter Zijlstra wrote:
> On Tue, Jun 14, 2016 at 06:48:08PM -0400, Waiman Long wrote:
>> even the reduced maximum of about 16k (32-bit) or 1G (64-bit) should
>> be more than enough for the foreseeable future.
> So what happens if I manage to create 16k+ threads on my 32bit kernel
> and get them all to do mmap() or so at the same time.
>
> That doesn't seem too far fetched.
>
> Then again, with double that (the current limit) that doesn't seem
> impossible either.
To hit the limit, we need to have all the threads calling down_write()
at exactly the same instance in time which, I think, is pretty hard to
do. Also, I don't believe you will ever see a 16k-cpu massive SMP system
running on 32-bit kernel. I can imagine such a system running on 64-bit
kernel, but certainly not 32-bit.
Cheers,
Longman
WARNING: multiple messages have this Message-ID (diff)
From: Waiman Long <waiman.long@hpe.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>, <linux-kernel@vger.kernel.org>,
<x86@kernel.org>, <linux-alpha@vger.kernel.org>,
<linux-ia64@vger.kernel.org>, <linux-s390@vger.kernel.org>,
<linux-arch@vger.kernel.org>, Davidlohr Bueso <dave@stgolabs.net>,
Jason Low <jason.low2@hp.com>, Dave Chinner <david@fromorbit.com>,
Scott J Norton <scott.norton@hpe.com>,
Douglas Hatch <doug.hatch@hpe.com>
Subject: Re: [RFC PATCH-tip v2 5/6] locking/rwsem: Change RWSEM_WAITING_BIAS for better disambiguation
Date: Wed, 15 Jun 2016 15:31:51 -0400 [thread overview]
Message-ID: <5761AD27.9020106@hpe.com> (raw)
In-Reply-To: <20160615174348.GT30921@twins.programming.kicks-ass.net>
On 06/15/2016 01:43 PM, Peter Zijlstra wrote:
> On Tue, Jun 14, 2016 at 06:48:08PM -0400, Waiman Long wrote:
>> even the reduced maximum of about 16k (32-bit) or 1G (64-bit) should
>> be more than enough for the foreseeable future.
> So what happens if I manage to create 16k+ threads on my 32bit kernel
> and get them all to do mmap() or so at the same time.
>
> That doesn't seem too far fetched.
>
> Then again, with double that (the current limit) that doesn't seem
> impossible either.
To hit the limit, we need to have all the threads calling down_write()
at exactly the same instance in time which, I think, is pretty hard to
do. Also, I don't believe you will ever see a 16k-cpu massive SMP system
running on 32-bit kernel. I can imagine such a system running on 64-bit
kernel, but certainly not 32-bit.
Cheers,
Longman
next prev parent reply other threads:[~2016-06-15 19:31 UTC|newest]
Thread overview: 101+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-14 22:48 [RFC PATCH-tip v2 0/6] locking/rwsem: Enable reader optimistic spinning Waiman Long
2016-06-14 22:48 ` Waiman Long
2016-06-14 22:48 ` [RFC PATCH-tip v2 1/6] locking/osq: Make lock/unlock proper acquire/release barrier Waiman Long
2016-06-14 22:48 ` Waiman Long
2016-06-15 8:04 ` Boqun Feng
2016-06-15 8:04 ` Boqun Feng
2016-06-15 17:18 ` Peter Zijlstra
2016-06-15 17:18 ` Peter Zijlstra
2016-06-15 19:01 ` Waiman Long
2016-06-15 19:01 ` Waiman Long
2016-06-15 19:01 ` Waiman Long
2016-06-16 2:19 ` Boqun Feng
2016-06-16 2:19 ` Boqun Feng
2016-06-16 10:16 ` Will Deacon
2016-06-16 10:16 ` Will Deacon
2016-06-16 21:35 ` Waiman Long
2016-06-16 21:35 ` Waiman Long
2016-06-16 21:35 ` Waiman Long
2016-06-17 0:48 ` Boqun Feng
2016-06-17 0:48 ` Boqun Feng
2016-06-17 15:26 ` Waiman Long
2016-06-17 15:26 ` Waiman Long
2016-06-17 15:26 ` Waiman Long
2016-06-17 15:45 ` Will Deacon
2016-06-17 15:45 ` Will Deacon
2016-06-17 18:17 ` Waiman Long
2016-06-17 18:17 ` Waiman Long
2016-06-17 18:17 ` Waiman Long
2016-06-18 8:46 ` Boqun Feng
2016-06-18 8:46 ` Boqun Feng
2016-06-20 7:59 ` Will Deacon
2016-06-20 7:59 ` Will Deacon
2016-06-15 16:56 ` Davidlohr Bueso
2016-06-15 16:56 ` Davidlohr Bueso
2016-06-15 17:12 ` Peter Zijlstra
2016-06-15 17:12 ` Peter Zijlstra
2016-06-15 18:27 ` Davidlohr Bueso
2016-06-15 18:27 ` Davidlohr Bueso
2016-06-15 18:40 ` Peter Zijlstra
2016-06-15 18:40 ` Peter Zijlstra
2016-06-15 18:56 ` Davidlohr Bueso
2016-06-15 18:56 ` Davidlohr Bueso
2016-06-17 1:11 ` Davidlohr Bueso
2016-06-17 1:11 ` Davidlohr Bueso
2016-06-17 14:28 ` Waiman Long
2016-06-17 14:28 ` Waiman Long
2016-06-17 14:28 ` Waiman Long
2016-06-17 16:29 ` Davidlohr Bueso
2016-06-17 16:29 ` Davidlohr Bueso
2016-06-17 16:46 ` Davidlohr Bueso
2016-06-17 16:46 ` Davidlohr Bueso
2016-06-15 19:08 ` Waiman Long
2016-06-15 19:08 ` Waiman Long
2016-06-15 19:08 ` Waiman Long
2016-06-15 20:04 ` Waiman Long
2016-06-15 20:04 ` Waiman Long
2016-06-15 20:04 ` Waiman Long
2016-06-15 21:59 ` Peter Zijlstra
2016-06-15 21:59 ` Peter Zijlstra
2016-06-14 22:48 ` [RFC PATCH-tip v2 2/6] locking/rwsem: Stop active read lock ASAP Waiman Long
2016-06-14 22:48 ` Waiman Long
2016-06-15 17:22 ` Peter Zijlstra
2016-06-15 17:22 ` Peter Zijlstra
2016-06-15 19:17 ` Waiman Long
2016-06-15 19:17 ` Waiman Long
2016-06-15 19:17 ` Waiman Long
2016-06-16 2:14 ` Davidlohr Bueso
2016-06-16 2:14 ` Davidlohr Bueso
2016-06-16 21:25 ` Waiman Long
2016-06-16 21:25 ` Waiman Long
2016-06-16 21:25 ` Waiman Long
2016-06-14 22:48 ` [RFC PATCH-tip v2 3/6] locking/rwsem: Enable count-based spinning on reader Waiman Long
2016-06-14 22:48 ` Waiman Long
2016-06-15 17:38 ` Peter Zijlstra
2016-06-15 17:38 ` Peter Zijlstra
2016-06-15 19:28 ` Waiman Long
2016-06-15 19:28 ` Waiman Long
2016-06-15 19:28 ` Waiman Long
2016-06-14 22:48 ` [RFC PATCH-tip v2 4/6] locking/rwsem: move down rwsem_down_read_failed function Waiman Long
2016-06-14 22:48 ` Waiman Long
2016-06-15 17:40 ` Peter Zijlstra
2016-06-15 17:40 ` Peter Zijlstra
2016-06-15 19:21 ` Waiman Long
2016-06-15 19:21 ` Waiman Long
2016-06-15 19:21 ` Waiman Long
2016-06-14 22:48 ` [RFC PATCH-tip v2 5/6] locking/rwsem: Change RWSEM_WAITING_BIAS for better disambiguation Waiman Long
2016-06-14 22:48 ` Waiman Long
2016-06-15 17:43 ` Peter Zijlstra
2016-06-15 17:43 ` Peter Zijlstra
2016-06-15 19:31 ` Waiman Long [this message]
2016-06-15 19:31 ` Waiman Long
2016-06-15 19:31 ` Waiman Long
2016-06-15 21:57 ` Peter Zijlstra
2016-06-15 21:57 ` Peter Zijlstra
2016-06-15 17:45 ` Peter Zijlstra
2016-06-15 17:45 ` Peter Zijlstra
2016-06-15 19:35 ` Waiman Long
2016-06-15 19:35 ` Waiman Long
2016-06-15 19:35 ` Waiman Long
2016-06-14 22:48 ` [RFC PATCH-tip v2 6/6] locking/rwsem: Enable spinning readers Waiman Long
2016-06-14 22:48 ` Waiman Long
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