search for: unhashing

On Wed, Apr 01, 2015 at 07:42:39PM +0200, Peter Zijlstra wrote: > > Hohumm.. time to think more I think ;-) > > So bear with me, I've not really pondered this well so it could be full > of holes (again). > > After the cmpxchg(&l->locked, _Q_LOCKED_VAL, _Q_SLOW_VAL) succeeds the > spin_unlock() must do the hash lookup, right? We can make the lookup > unhash.

On Wed, Apr 01, 2015 at 07:42:39PM +0200, Peter Zijlstra wrote: > > Hohumm.. time to think more I think ;-) > > So bear with me, I've not really pondered this well so it could be full > of holes (again). > > After the cmpxchg(&l->locked, _Q_LOCKED_VAL, _Q_SLOW_VAL) succeeds the > spin_unlock() must do the hash lookup, right? We can make the lookup > unhash.

...lookup and we must > >>unhash. > >The idea being that the result is that any lookup is guaranteed to find > >an entry, which reduces our worst case lookup cost to whatever the worst > >case insertion cost was. > > > > I think it doesn't matter who did the unhashing. Multiple independent locks > can be hashed to the same value. Since they can be unhashed independently, > there is no way to know whether you have checked all the possible buckets. oh but the crux is that you guarantee a lookup will find an entry. it will never need to iterate the entire ar...

...lookup and we must > >>unhash. > >The idea being that the result is that any lookup is guaranteed to find > >an entry, which reduces our worst case lookup cost to whatever the worst > >case insertion cost was. > > > > I think it doesn't matter who did the unhashing. Multiple independent locks > can be hashed to the same value. Since they can be unhashed independently, > there is no way to know whether you have checked all the possible buckets. oh but the crux is that you guarantee a lookup will find an entry. it will never need to iterate the entire ar...

Currently we only print mstb/port pointer addresses in our malloc and topology refcount functions using the hashed-by-default %p, but unfortunately if you're trying to debug a use-after-free error caused by a refcounting error then this really isn't terribly useful. On the other hand though, everything in the rest of the DP MST helpers uses hashed pointer values as well and probably

On Tue, Sep 03, 2019 at 04:46:04PM -0400, Lyude Paul wrote: > Currently we only print mstb/port pointer addresses in our malloc and > topology refcount functions using the hashed-by-default %p, but > unfortunately if you're trying to debug a use-after-free error caused by > a refcounting error then this really isn't terribly useful. On the other > hand though, everything in

...ils the unlock will not do the lookup and we must >> unhash. > The idea being that the result is that any lookup is guaranteed to find > an entry, which reduces our worst case lookup cost to whatever the worst > case insertion cost was. > I think it doesn't matter who did the unhashing. Multiple independent locks can be hashed to the same value. Since they can be unhashed independently, there is no way to know whether you have checked all the possible buckets. -Longman

...t >>>> unhash. >>> The idea being that the result is that any lookup is guaranteed to find >>> an entry, which reduces our worst case lookup cost to whatever the worst >>> case insertion cost was. >>> >> I think it doesn't matter who did the unhashing. Multiple independent locks >> can be hashed to the same value. Since they can be unhashed independently, >> there is no way to know whether you have checked all the possible buckets. > oh but the crux is that you guarantee a lookup will find an entry. it will > never need to iter...

On Thu, Apr 02, 2015 at 12:28:30PM -0400, Waiman Long wrote: > On 04/01/2015 05:03 PM, Peter Zijlstra wrote: > >On Wed, Apr 01, 2015 at 03:58:58PM -0400, Waiman Long wrote: > >>On 04/01/2015 02:48 PM, Peter Zijlstra wrote: > >>I am sorry that I don't quite get what you mean here. My point is that in > >>the hashing step, a cpu will need to scan an empty

On Thu, Apr 02, 2015 at 12:28:30PM -0400, Waiman Long wrote: > On 04/01/2015 05:03 PM, Peter Zijlstra wrote: > >On Wed, Apr 01, 2015 at 03:58:58PM -0400, Waiman Long wrote: > >>On 04/01/2015 02:48 PM, Peter Zijlstra wrote: > >>I am sorry that I don't quite get what you mean here. My point is that in > >>the hashing step, a cpu will need to scan an empty

On Wed, Apr 01, 2015 at 12:20:30PM -0400, Waiman Long wrote: > After more careful reading, I think the assumption that the presence of an > unused bucket means there is no match is not true. Consider the scenario: > > 1. cpu 0 puts lock1 into hb[0] > 2. cpu 1 puts lock2 into hb[1] > 3. cpu 2 clears hb[0] > 4. cpu 3 looks for lock2 and doesn't find it Hmm, yes. The only

On Wed, Apr 01, 2015 at 12:20:30PM -0400, Waiman Long wrote: > After more careful reading, I think the assumption that the presence of an > unused bucket means there is no match is not true. Consider the scenario: > > 1. cpu 0 puts lock1 into hb[0] > 2. cpu 1 puts lock2 into hb[1] > 3. cpu 2 clears hb[0] > 4. cpu 3 looks for lock2 and doesn't find it Hmm, yes. The only

On Thu, Apr 09, 2015 at 05:41:44PM -0400, Waiman Long wrote: > >>+static void pv_wait_head(struct qspinlock *lock, struct mcs_spinlock *node) > >>+{ > >>+ struct __qspinlock *l = (void *)lock; > >>+ struct qspinlock **lp = NULL; > >>+ struct pv_node *pn = (struct pv_node *)node; > >>+ int slow_set = false; > >>+ int loop; >

On Thu, Apr 09, 2015 at 05:41:44PM -0400, Waiman Long wrote: > >>+static void pv_wait_head(struct qspinlock *lock, struct mcs_spinlock *node) > >>+{ > >>+ struct __qspinlock *l = (void *)lock; > >>+ struct qspinlock **lp = NULL; > >>+ struct pv_node *pn = (struct pv_node *)node; > >>+ int slow_set = false; > >>+ int loop; >

On Wed, May 25, 2016 at 04:18:08PM +0800, Pan Xinhui wrote: > cmpxchg_release is light-wight than cmpxchg, we can gain a better > performace then. On some arch like ppc, barrier impact the performace > too much. > > Suggested-by: Boqun Feng <boqun.feng at gmail.com> > Signed-off-by: Pan Xinhui <xinhui.pan at linux.vnet.ibm.com> > --- >

On Wed, May 25, 2016 at 04:18:08PM +0800, Pan Xinhui wrote: > cmpxchg_release is light-wight than cmpxchg, we can gain a better > performace then. On some arch like ppc, barrier impact the performace > too much. > > Suggested-by: Boqun Feng <boqun.feng at gmail.com> > Signed-off-by: Pan Xinhui <xinhui.pan at linux.vnet.ibm.com> > --- >

Hi list members, just tried to get some old records out of my known_hosts, which is 'HashKnownHosts yes'. Is there a way to unhash host names and/or IPs? Google tells about, how to add hosts, but not the opposite, may be I miss some thing. Is this does not work at all, is there a best practice for cleaning old hosts and keys out? Thanks, Martin! -- Martin GnuPG Key Fingerprint, KeyID

On Thu, Apr 02, 2015 at 07:20:57PM +0200, Peter Zijlstra wrote: > pv_wait_head(): > > pv_hash() > /* MB as per cmpxchg */ > cmpxchg(&l->locked, _Q_LOCKED_VAL, _Q_SLOW_VAL); > > VS > > __pv_queue_spin_unlock(): > > if (xchg(&l->locked, 0) != _Q_SLOW_VAL) > return; > > /* MB as per xchg */ > pv_hash_find(lock); > >

The following benchmarks have been obtained using the TextMate manual as the input source: <http://macromates.com/textmate/manual/source.tbz> Using PHP Markdown, parsing the 24 files separately (with the reference file appended to each of them), I get this (on an iBook G4 1.2 Ghz): Total Avg. Min. Q1. Med. Q3. Max. Parse Time (ms):