* [PATCH 01/22] powerpc, workqueue: Use alloc_ordered_workqueue() to create ordered workqueues [not found] <20230421025046.4008499-1-tj@kernel.org> @ 2023-04-21 2:50 ` Tejun Heo 2023-04-21 5:20 ` Michael Ellerman 2023-05-08 23:55 ` Tejun Heo 0 siblings, 2 replies; 3+ messages in thread From: Tejun Heo @ 2023-04-21 2:50 UTC (permalink / raw) To: jiangshanlai Cc: Nathan Lynch, kernel-team, linux-kernel, Nicholas Piggin, Tejun Heo, linuxppc-dev BACKGROUND ========== When multiple work items are queued to a workqueue, their execution order doesn't match the queueing order. They may get executed in any order and simultaneously. When fully serialized execution - one by one in the queueing order - is needed, an ordered workqueue should be used which can be created with alloc_ordered_workqueue(). However, alloc_ordered_workqueue() was a later addition. Before it, an ordered workqueue could be obtained by creating an UNBOUND workqueue with @max_active==1. This originally was an implementation side-effect which was broken by 4c16bd327c74 ("workqueue: restore WQ_UNBOUND/max_active==1 to be ordered"). Because there were users that depended on the ordered execution, 5c0338c68706 ("workqueue: restore WQ_UNBOUND/max_active==1 to be ordered") made workqueue allocation path to implicitly promote UNBOUND workqueues w/ @max_active==1 to ordered workqueues. While this has worked okay, overloading the UNBOUND allocation interface this way creates other issues. It's difficult to tell whether a given workqueue actually needs to be ordered and users that legitimately want a min concurrency level wq unexpectedly gets an ordered one instead. With planned UNBOUND workqueue updates to improve execution locality and more prevalence of chiplet designs which can benefit from such improvements, this isn't a state we wanna be in forever. This patch series audits all callsites that create an UNBOUND workqueue w/ @max_active==1 and converts them to alloc_ordered_workqueue() as necessary. WHAT TO LOOK FOR ================ The conversions are from alloc_workqueue(WQ_UNBOUND | flags, 1, args..) to alloc_ordered_workqueue(flags, args...) which don't cause any functional changes. If you know that fully ordered execution is not ncessary, please let me know. I'll drop the conversion and instead add a comment noting the fact to reduce confusion while conversion is in progress. If you aren't fully sure, it's completely fine to let the conversion through. The behavior will stay exactly the same and we can always reconsider later. As there are follow-up workqueue core changes, I'd really appreciate if the patch can be routed through the workqueue tree w/ your acks. Thanks. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Christophe Leroy <christophe.leroy@csgroup.eu> Cc: Nathan Lynch <nathanl@linux.ibm.com> Cc: linuxppc-dev@lists.ozlabs.org --- arch/powerpc/kernel/tau_6xx.c | 2 +- arch/powerpc/platforms/pseries/dlpar.c | 3 +-- 2 files changed, 2 insertions(+), 3 deletions(-) diff --git a/arch/powerpc/kernel/tau_6xx.c b/arch/powerpc/kernel/tau_6xx.c index 828d0f4106d2..cba6dd15de3b 100644 --- a/arch/powerpc/kernel/tau_6xx.c +++ b/arch/powerpc/kernel/tau_6xx.c @@ -200,7 +200,7 @@ static int __init TAU_init(void) tau_int_enable = IS_ENABLED(CONFIG_TAU_INT) && !strcmp(cur_cpu_spec->platform, "ppc750"); - tau_workq = alloc_workqueue("tau", WQ_UNBOUND, 1); + tau_workq = alloc_ordered_workqueue("tau", 0); if (!tau_workq) return -ENOMEM; diff --git a/arch/powerpc/platforms/pseries/dlpar.c b/arch/powerpc/platforms/pseries/dlpar.c index 75ffdbcd2865..e9117b03807e 100644 --- a/arch/powerpc/platforms/pseries/dlpar.c +++ b/arch/powerpc/platforms/pseries/dlpar.c @@ -564,8 +564,7 @@ int __init dlpar_workqueue_init(void) if (pseries_hp_wq) return 0; - pseries_hp_wq = alloc_workqueue("pseries hotplug workqueue", - WQ_UNBOUND, 1); + pseries_hp_wq = alloc_ordered_workqueue("pseries hotplug workqueue", 0); return pseries_hp_wq ? 0 : -ENOMEM; } -- 2.40.0 ^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH 01/22] powerpc, workqueue: Use alloc_ordered_workqueue() to create ordered workqueues 2023-04-21 2:50 ` [PATCH 01/22] powerpc, workqueue: Use alloc_ordered_workqueue() to create ordered workqueues Tejun Heo @ 2023-04-21 5:20 ` Michael Ellerman 2023-05-08 23:55 ` Tejun Heo 1 sibling, 0 replies; 3+ messages in thread From: Michael Ellerman @ 2023-04-21 5:20 UTC (permalink / raw) To: Tejun Heo, jiangshanlai Cc: Nathan Lynch, kernel-team, linux-kernel, Nicholas Piggin, Tejun Heo, linuxppc-dev Tejun Heo <tj@kernel.org> writes: > BACKGROUND > ========== > > When multiple work items are queued to a workqueue, their execution order > doesn't match the queueing order. They may get executed in any order and > simultaneously. When fully serialized execution - one by one in the queueing > order - is needed, an ordered workqueue should be used which can be created > with alloc_ordered_workqueue(). > > However, alloc_ordered_workqueue() was a later addition. Before it, an > ordered workqueue could be obtained by creating an UNBOUND workqueue with > @max_active==1. This originally was an implementation side-effect which was > broken by 4c16bd327c74 ("workqueue: restore WQ_UNBOUND/max_active==1 to be > ordered"). Because there were users that depended on the ordered execution, > 5c0338c68706 ("workqueue: restore WQ_UNBOUND/max_active==1 to be ordered") > made workqueue allocation path to implicitly promote UNBOUND workqueues w/ > @max_active==1 to ordered workqueues. > > While this has worked okay, overloading the UNBOUND allocation interface > this way creates other issues. It's difficult to tell whether a given > workqueue actually needs to be ordered and users that legitimately want a > min concurrency level wq unexpectedly gets an ordered one instead. With > planned UNBOUND workqueue updates to improve execution locality and more > prevalence of chiplet designs which can benefit from such improvements, this > isn't a state we wanna be in forever. > > This patch series audits all callsites that create an UNBOUND workqueue w/ > @max_active==1 and converts them to alloc_ordered_workqueue() as necessary. > > WHAT TO LOOK FOR > ================ > > The conversions are from > > alloc_workqueue(WQ_UNBOUND | flags, 1, args..) > > to > > alloc_ordered_workqueue(flags, args...) > > which don't cause any functional changes. If you know that fully ordered > execution is not ncessary, please let me know. I'll drop the conversion and > instead add a comment noting the fact to reduce confusion while conversion > is in progress. > > If you aren't fully sure, it's completely fine to let the conversion > through. The behavior will stay exactly the same and we can always > reconsider later. > > As there are follow-up workqueue core changes, I'd really appreciate if the > patch can be routed through the workqueue tree w/ your acks. Thanks. > > Signed-off-by: Tejun Heo <tj@kernel.org> > Cc: Michael Ellerman <mpe@ellerman.id.au> > Cc: Nicholas Piggin <npiggin@gmail.com> > Cc: Christophe Leroy <christophe.leroy@csgroup.eu> > Cc: Nathan Lynch <nathanl@linux.ibm.com> > Cc: linuxppc-dev@lists.ozlabs.org > --- > arch/powerpc/kernel/tau_6xx.c | 2 +- > arch/powerpc/platforms/pseries/dlpar.c | 3 +-- > 2 files changed, 2 insertions(+), 3 deletions(-) Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc) > diff --git a/arch/powerpc/kernel/tau_6xx.c b/arch/powerpc/kernel/tau_6xx.c > index 828d0f4106d2..cba6dd15de3b 100644 > --- a/arch/powerpc/kernel/tau_6xx.c > +++ b/arch/powerpc/kernel/tau_6xx.c > @@ -200,7 +200,7 @@ static int __init TAU_init(void) > tau_int_enable = IS_ENABLED(CONFIG_TAU_INT) && > !strcmp(cur_cpu_spec->platform, "ppc750"); > > - tau_workq = alloc_workqueue("tau", WQ_UNBOUND, 1); > + tau_workq = alloc_ordered_workqueue("tau", 0); > if (!tau_workq) > return -ENOMEM; > > diff --git a/arch/powerpc/platforms/pseries/dlpar.c b/arch/powerpc/platforms/pseries/dlpar.c > index 75ffdbcd2865..e9117b03807e 100644 > --- a/arch/powerpc/platforms/pseries/dlpar.c > +++ b/arch/powerpc/platforms/pseries/dlpar.c > @@ -564,8 +564,7 @@ int __init dlpar_workqueue_init(void) > if (pseries_hp_wq) > return 0; > > - pseries_hp_wq = alloc_workqueue("pseries hotplug workqueue", > - WQ_UNBOUND, 1); > + pseries_hp_wq = alloc_ordered_workqueue("pseries hotplug workqueue", 0); > > return pseries_hp_wq ? 0 : -ENOMEM; > } The change log of commit 9054619ef54a ("powerpc/pseries: Add pseries hotplug workqueue") makes it fairly clear that this code does explicitly want an ordered queue. cheers ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH 01/22] powerpc, workqueue: Use alloc_ordered_workqueue() to create ordered workqueues 2023-04-21 2:50 ` [PATCH 01/22] powerpc, workqueue: Use alloc_ordered_workqueue() to create ordered workqueues Tejun Heo 2023-04-21 5:20 ` Michael Ellerman @ 2023-05-08 23:55 ` Tejun Heo 1 sibling, 0 replies; 3+ messages in thread From: Tejun Heo @ 2023-05-08 23:55 UTC (permalink / raw) To: jiangshanlai Cc: Nathan Lynch, kernel-team, linux-kernel, Nicholas Piggin, linuxppc-dev Applied to wq/for-6.5-cleanup-ordered. Thanks. -- tejun ^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2023-05-08 23:56 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
[not found] <20230421025046.4008499-1-tj@kernel.org>
2023-04-21 2:50 ` [PATCH 01/22] powerpc, workqueue: Use alloc_ordered_workqueue() to create ordered workqueues Tejun Heo
2023-04-21 5:20 ` Michael Ellerman
2023-05-08 23:55 ` Tejun Heo
This is a public inbox, see mirroring instructions for how to clone and mirror all data and code used for this inbox; as well as URLs for NNTP newsgroup(s).