Date: Thu, 27 Sep 2012 11:29:20 -0500 From: Alan Cox <alc@rice.edu> To: John-Mark Gurney <jmg@funkthat.com> Cc: "arm@freebsd.org" <arm@freebsd.org> Subject: Re: arm pmap locking Message-ID: <50647EE0.6010900@rice.edu> In-Reply-To: <20120926061340.GL19036@funkthat.com> References: <1346350374.1140.525.camel@revolution.hippie.lan> <5045351F.6060201@rice.edu> <1346723041.1140.602.camel@revolution.hippie.lan> <504B85BE.3030101@rice.edu> <1347316458.1137.41.camel@revolution.hippie.lan> <504F8BAC.4040902@rice.edu> <20120915045040.GZ58312@funkthat.com> <5054D69B.40209@rice.edu> <20120917033308.GB58312@funkthat.com> <5061D2AA.3000100@rice.edu> <20120926061340.GL19036@funkthat.com>
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On 09/26/2012 01:13, John-Mark Gurney wrote:
> Alan Cox wrote this message on Tue, Sep 25, 2012 at 10:50 -0500:
>> On 09/16/2012 22:33, John-Mark Gurney wrote:
>>> Still getting the LOR.. It always right after boot.. after trying
>>> to mount root and warning about no time-of-day clock, but before setting
>>> hostuuid..
>> Could you please try the attached patch on your armv6 BEAGLEBONE? My
>> hope is that this addresses the root cause of the LORs involving the
>> pmap lock.
> Good news... That patch boots and doesn't have the LOR...
>
> FreeBSD 10.0-CURRENT #10 r240947M: Mon Sep 24 17:01:11 PDT 2012
> jmg@pcbsd-779:/usr/obj/arm.armv6/usr/src.HEAD/sys/helium arm
>
> [...]
>
> Trying to mount root from ufs:mmcsd0s2 []...
> warning: no time-of-day clock registered, system time will not be set accurately
> Setting hostuuid: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx.
>
> Thanks for your work tracking it down!
>
Great. Now that the LOR is out of the way, let's try further
simplifications to the locking. I don't believe that
pmap_alloc_l2_bucket() needs to unlock and relock around every
allocation. Here is another patch to eliminate that. Also, the patch
replaces an explicit bzero() call with M_ZERO.
Alan
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Index: arm/arm/pmap-v6.c
===================================================================
--- arm/arm/pmap-v6.c (revision 240983)
+++ arm/arm/pmap-v6.c (working copy)
@@ -607,36 +607,20 @@ pmap_alloc_l2_bucket(pmap_t pm, vm_offset_t va)
l1idx = L1_IDX(va);
PMAP_ASSERT_LOCKED(pm);
- rw_assert(&pvh_global_lock, RA_WLOCKED);
if ((l2 = pm->pm_l2[L2_IDX(l1idx)]) == NULL) {
/*
* No mapping at this address, as there is
* no entry in the L1 table.
* Need to allocate a new l2_dtable.
*/
- PMAP_UNLOCK(pm);
- rw_wunlock(&pvh_global_lock);
- if ((l2 = uma_zalloc(l2table_zone, M_NOWAIT)) == NULL) {
- rw_wlock(&pvh_global_lock);
- PMAP_LOCK(pm);
+ l2 = uma_zalloc(l2table_zone, M_NOWAIT | M_ZERO);
+ if (l2 == NULL)
return (NULL);
- }
- rw_wlock(&pvh_global_lock);
- PMAP_LOCK(pm);
- if (pm->pm_l2[L2_IDX(l1idx)] != NULL) {
- /*
- * Someone already allocated the l2_dtable while
- * we were doing the same.
- */
- uma_zfree(l2table_zone, l2);
- l2 = pm->pm_l2[L2_IDX(l1idx)];
- } else {
- bzero(l2, sizeof(*l2));
- /*
- * Link it into the parent pmap
- */
- pm->pm_l2[L2_IDX(l1idx)] = l2;
- }
+
+ /*
+ * Link it into the parent pmap.
+ */
+ pm->pm_l2[L2_IDX(l1idx)] = l2;
}
l2b = &l2->l2_bucket[L2_BUCKET(l1idx)];
@@ -651,17 +635,7 @@ pmap_alloc_l2_bucket(pmap_t pm, vm_offset_t va)
* No L2 page table has been allocated. Chances are, this
* is because we just allocated the l2_dtable, above.
*/
- PMAP_UNLOCK(pm);
- rw_wunlock(&pvh_global_lock);
ptep = uma_zalloc(l2zone, M_NOWAIT);
- rw_wlock(&pvh_global_lock);
- PMAP_LOCK(pm);
- if (l2b->l2b_kva != 0) {
- /* We lost the race. */
- uma_zfree(l2zone, ptep);
- return (l2b);
- }
- l2b->l2b_phys = vtophys(ptep);
if (ptep == NULL) {
/*
* Oops, no more L2 page tables available at this
@@ -677,6 +651,7 @@ pmap_alloc_l2_bucket(pmap_t pm, vm_offset_t va)
l2->l2_occupancy++;
l2b->l2b_kva = ptep;
+ l2b->l2b_phys = pmap_kextract((vm_offset_t)ptep);
l2b->l2b_l1idx = l1idx;
}
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