On 05/30/2014 04:15 AM, Waiman Long wrote:
On 05/28/2014 08:16 AM, Raghavendra K T wrote:
- we need an intelligent way to nullify the effect of batching for
baremetal
(because extra cmpxchg is not required).
To do this, you will need to have 2 slightly different algorithms
depending on the p
On 05/28/2014 08:16 AM, Raghavendra K T wrote:
TODO:
- we need an intelligent way to nullify the effect of batching for baremetal
(because extra cmpxchg is not required).
To do this, you will need to have 2 slightly different algorithms
depending on the paravirt_ticketlocks_enabled jump lab
On 05/29/2014 12:16 PM, Peter Zijlstra wrote:
On Wed, May 28, 2014 at 05:46:39PM +0530, Raghavendra K T wrote:
In virtualized environment there are mainly three problems
related to spinlocks that affect performance.
1. LHP (lock holder preemption)
2. Lock Waiter Preemption (LWP)
3. Starvation/fa
On 05/29/2014 03:25 AM, Rik van Riel wrote:
On 05/28/2014 08:16 AM, Raghavendra K T wrote:
This patch looks very promising.
Thank you Rik.
[...]
- My kernbench/ebizzy test on baremetal (32 cpu +ht sandybridge) did not seem to
show the impact of extra cmpxchg. but there should be effect o
On Wed, May 28, 2014 at 05:46:39PM +0530, Raghavendra K T wrote:
> In virtualized environment there are mainly three problems
> related to spinlocks that affect performance.
> 1. LHP (lock holder preemption)
> 2. Lock Waiter Preemption (LWP)
> 3. Starvation/fairness
>
> Though ticketlocks solve t
On 05/28/2014 06:19 PM, Linus Torvalds wrote:
> If somebody has a P4 still, that's likely the worst case by far.
I'm sure cmpxchg isn't the only thing making P4 the worst case :)
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On Wed, 28 May 2014, Linus Torvalds wrote:
>
> If somebody has a P4 still, that's likely the worst case by far.
I do, but I'm only using it during winter and only if the ia64 machine
does not provide sufficient heating. So you have to wait at least half
a year until I'm able to test it.
_
On Wed, May 28, 2014 at 2:55 PM, Rik van Riel wrote:
>
> Or maybe cmpxchg is cheap once you already own the cache line
> exclusively?
A locked cmpxchg ends up being anything between ~15-50 cycles
depending on microarchitecture if things are already exclusively in
the cache (with the P4 being an o
On 05/28/2014 08:16 AM, Raghavendra K T wrote:
This patch looks very promising.
> TODO:
> - we need an intelligent way to nullify the effect of batching for baremetal
> (because extra cmpxchg is not required).
On (larger?) NUMA systems, the unfairness may be a nice performance
benefit, reducing
In virtualized environment there are mainly three problems
related to spinlocks that affect performance.
1. LHP (lock holder preemption)
2. Lock Waiter Preemption (LWP)
3. Starvation/fairness
Though ticketlocks solve the fairness problem, it worsens LWP, LHP problems.
pv-ticketlocks tried to addr
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