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[PATCH v6 09/12] softmmu/physmem: Don't use atomic operations in ram_blo
From: |
David Hildenbrand |
Subject: |
[PATCH v6 09/12] softmmu/physmem: Don't use atomic operations in ram_block_discard_(disable|require) |
Date: |
Mon, 22 Feb 2021 12:57:05 +0100 |
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>
---
softmmu/physmem.c | 70 ++++++++++++++++++++++++++---------------------
1 file changed, 39 insertions(+), 31 deletions(-)
diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index 19e0aa9836..6550217c26 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -3677,56 +3677,64 @@ 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_requirers;
+static unsigned int ram_block_discard_disablers;
+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_disablers--;
+ } else if (!ram_block_discard_requirers) {
+ ram_block_discard_disablers++;
+ } 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_requirers--;
+ } else if (!ram_block_discard_disablers) {
+ ram_block_discard_requirers++;
+ } 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_disablers);
}
bool ram_block_discard_is_required(void)
{
- return qatomic_read(&ram_block_discard_disabled) < 0;
+ return qatomic_read(&ram_block_discard_requirers);
}
--
2.29.2
- [PATCH v6 03/12] virtio-mem: Don't report errors when ram_block_discard_range() fails, (continued)
[PATCH v6 06/12] vfio: Query and store the maximum number of possible DMA mappings, David Hildenbrand, 2021/02/22
[PATCH v6 07/12] vfio: Sanity check maximum number of DMA mappings with RamDiscardMgr, David Hildenbrand, 2021/02/22
[PATCH v6 08/12] vfio: Support for RamDiscardMgr in the vIOMMU case, David Hildenbrand, 2021/02/22
[PATCH v6 09/12] softmmu/physmem: Don't use atomic operations in ram_block_discard_(disable|require),
David Hildenbrand <=
- Re: [PATCH v6 09/12] softmmu/physmem: Don't use atomic operations in ram_block_discard_(disable|require), Paolo Bonzini, 2021/02/22
- Re: [PATCH v6 09/12] softmmu/physmem: Don't use atomic operations in ram_block_discard_(disable|require), David Hildenbrand, 2021/02/22
- Re: [PATCH v6 09/12] softmmu/physmem: Don't use atomic operations in ram_block_discard_(disable|require), Paolo Bonzini, 2021/02/22
- Re: [PATCH v6 09/12] softmmu/physmem: Don't use atomic operations in ram_block_discard_(disable|require), David Hildenbrand, 2021/02/22
- Re: [PATCH v6 09/12] softmmu/physmem: Don't use atomic operations in ram_block_discard_(disable|require), Paolo Bonzini, 2021/02/22
- Re: [PATCH v6 09/12] softmmu/physmem: Don't use atomic operations in ram_block_discard_(disable|require), David Hildenbrand, 2021/02/23
- Re: [PATCH v6 09/12] softmmu/physmem: Don't use atomic operations in ram_block_discard_(disable|require), Paolo Bonzini, 2021/02/23
[PATCH v6 10/12] softmmu/physmem: Extend ram_block_discard_(require|disable) by two discard types, David Hildenbrand, 2021/02/22
[PATCH v6 11/12] virtio-mem: Require only coordinated discards, David Hildenbrand, 2021/02/22
[PATCH v6 12/12] vfio: Disable only uncoordinated discards for VFIO_TYPE1 iommus, David Hildenbrand, 2021/02/22