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[PULL 12/15] softmmu/physmem: Don't use atomic operations in ram_block_d
From: |
Eduardo Habkost |
Subject: |
[PULL 12/15] softmmu/physmem: Don't use atomic operations in ram_block_discard_(disable|require) |
Date: |
Wed, 7 Jul 2021 15:32:38 -0400 |
From: David Hildenbrand <david@redhat.com>
We have users in migration context that don't hold the BQL (when
finishing migration). To prepare for further changes, use a dedicated mutex
instead of atomic operations. Keep using qatomic_read ("READ_ONCE") for the
functions that only extract the current state (e.g., used by
virtio-balloon), locking isn't necessary.
While at it, split up the counter into two variables to make it easier
to understand.
Suggested-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Auger Eric <eric.auger@redhat.com>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: teawater <teawaterz@linux.alibaba.com>
Cc: Marek Kedzierski <mkedzier@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20210413095531.25603-11-david@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
softmmu/physmem.c | 70 ++++++++++++++++++++++++++---------------------
1 file changed, 39 insertions(+), 31 deletions(-)
diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index 9b171c9dbe5..f1275b61f84 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -3684,56 +3684,64 @@ void mtree_print_dispatch(AddressSpaceDispatch *d,
MemoryRegion *root)
}
}
-/*
- * If positive, discarding RAM is disabled. If negative, discarding RAM is
- * required to work and cannot be disabled.
- */
-static int ram_block_discard_disabled;
+static unsigned int ram_block_discard_required_cnt;
+static unsigned int ram_block_discard_disabled_cnt;
+static QemuMutex ram_block_discard_disable_mutex;
+
+static void ram_block_discard_disable_mutex_lock(void)
+{
+ static gsize initialized;
+
+ if (g_once_init_enter(&initialized)) {
+ qemu_mutex_init(&ram_block_discard_disable_mutex);
+ g_once_init_leave(&initialized, 1);
+ }
+ qemu_mutex_lock(&ram_block_discard_disable_mutex);
+}
+
+static void ram_block_discard_disable_mutex_unlock(void)
+{
+ qemu_mutex_unlock(&ram_block_discard_disable_mutex);
+}
int ram_block_discard_disable(bool state)
{
- int old;
+ int ret = 0;
+ ram_block_discard_disable_mutex_lock();
if (!state) {
- qatomic_dec(&ram_block_discard_disabled);
- return 0;
+ ram_block_discard_disabled_cnt--;
+ } else if (!ram_block_discard_required_cnt) {
+ ram_block_discard_disabled_cnt++;
+ } else {
+ ret = -EBUSY;
}
-
- do {
- old = qatomic_read(&ram_block_discard_disabled);
- if (old < 0) {
- return -EBUSY;
- }
- } while (qatomic_cmpxchg(&ram_block_discard_disabled,
- old, old + 1) != old);
- return 0;
+ ram_block_discard_disable_mutex_unlock();
+ return ret;
}
int ram_block_discard_require(bool state)
{
- int old;
+ int ret = 0;
+ ram_block_discard_disable_mutex_lock();
if (!state) {
- qatomic_inc(&ram_block_discard_disabled);
- return 0;
+ ram_block_discard_required_cnt--;
+ } else if (!ram_block_discard_disabled_cnt) {
+ ram_block_discard_required_cnt++;
+ } else {
+ ret = -EBUSY;
}
-
- do {
- old = qatomic_read(&ram_block_discard_disabled);
- if (old > 0) {
- return -EBUSY;
- }
- } while (qatomic_cmpxchg(&ram_block_discard_disabled,
- old, old - 1) != old);
- return 0;
+ ram_block_discard_disable_mutex_unlock();
+ return ret;
}
bool ram_block_discard_is_disabled(void)
{
- return qatomic_read(&ram_block_discard_disabled) > 0;
+ return qatomic_read(&ram_block_discard_disabled_cnt);
}
bool ram_block_discard_is_required(void)
{
- return qatomic_read(&ram_block_discard_disabled) < 0;
+ return qatomic_read(&ram_block_discard_required_cnt);
}
--
2.31.1
- [PULL 04/15] memory: Helpers to copy/free a MemoryRegionSection, (continued)
- [PULL 04/15] memory: Helpers to copy/free a MemoryRegionSection, Eduardo Habkost, 2021/07/07
- [PULL 03/15] memory: Introduce RamDiscardManager for RAM memory regions, Eduardo Habkost, 2021/07/07
- [PULL 01/15] vmbus: Don't make QOM property registration conditional, Eduardo Habkost, 2021/07/07
- [PULL 05/15] virtio-mem: Factor out traversing unplugged ranges, Eduardo Habkost, 2021/07/07
- [PULL 06/15] virtio-mem: Don't report errors when ram_block_discard_range() fails, Eduardo Habkost, 2021/07/07
- [PULL 07/15] virtio-mem: Implement RamDiscardManager interface, Eduardo Habkost, 2021/07/07
- [PULL 09/15] vfio: Query and store the maximum number of possible DMA mappings, Eduardo Habkost, 2021/07/07
- [PULL 10/15] vfio: Sanity check maximum number of DMA mappings with RamDiscardManager, Eduardo Habkost, 2021/07/07
- [PULL 08/15] vfio: Support for RamDiscardManager in the !vIOMMU case, Eduardo Habkost, 2021/07/07
- [PULL 11/15] vfio: Support for RamDiscardManager in the vIOMMU case, Eduardo Habkost, 2021/07/07
- [PULL 12/15] softmmu/physmem: Don't use atomic operations in ram_block_discard_(disable|require),
Eduardo Habkost <=
- [PULL 13/15] softmmu/physmem: Extend ram_block_discard_(require|disable) by two discard types, Eduardo Habkost, 2021/07/07
- [PULL 15/15] vfio: Disable only uncoordinated discards for VFIO_TYPE1 iommus, Eduardo Habkost, 2021/07/07
- [PULL 14/15] virtio-mem: Require only coordinated discards, Eduardo Habkost, 2021/07/07
- Re: [PULL 00/15] Machine queue, 2021-07-07, Peter Maydell, 2021/07/08