Olaf Hering
2011-Sep-05 09:18 UTC
[Xen-devel] [PATCH] mem_event: add ref counting for free requestslots
# HG changeset patch
# User Olaf Hering <olaf@aepfle.de>
# Date 1315214140 -7200
# Node ID b2c8dacb2dc08bd93e4926eb0c2c7823d40e2174
# Parent f1349a968a5ac5577d67ad4a3f3490c580dbe264
mem_event: add ref counting for free requestslots
If mem_event_check_ring() is called by many vcpus at the same time before
any of them called also mem_event_put_request(), all of the callers must
assume there are enough free slots available in the ring.
Record the number of request producers in mem_event_check_ring() to keep
track of available free slots.
Add a new mem_event_put_req_producers() function to release a request
attempt made in mem_event_check_ring(). Its required for
p2m_mem_paging_populate() because that function can only modify the p2m type
if there are free request slots. But in some cases p2m_mem_paging_populate()
does not actually have to produce another request when it is known that the
same request was already made earlier by a different vcpu.
mem_event_check_ring() can not return a reference to a free request slot
because there could be multiple references for different vcpus and the order
of mem_event_put_request() calls is not known. As a result, incomplete
requests could be consumed by the ring user.
Signed-off-by: Olaf Hering <olaf@aepfle.de>
diff -r f1349a968a5a -r b2c8dacb2dc0 xen/arch/x86/mm/mem_event.c
--- a/xen/arch/x86/mm/mem_event.c
+++ b/xen/arch/x86/mm/mem_event.c
@@ -37,8 +37,6 @@
#define mem_event_ring_lock(_d)
spin_lock(&(_d)->mem_event.ring_lock)
#define mem_event_ring_unlock(_d)
spin_unlock(&(_d)->mem_event.ring_lock)
-#define MEM_EVENT_RING_THRESHOLD 4
-
static int mem_event_enable(struct domain *d, mfn_t ring_mfn, mfn_t shared_mfn)
{
int rc;
@@ -109,6 +107,7 @@ void mem_event_put_request(struct domain
req_prod++;
/* Update ring */
+ d->mem_event.req_producers--;
front_ring->req_prod_pvt = req_prod;
RING_PUSH_REQUESTS(front_ring);
@@ -153,11 +152,18 @@ void mem_event_mark_and_pause(struct vcp
vcpu_sleep_nosync(v);
}
+void mem_event_put_req_producers(struct domain *d)
+{
+ mem_event_ring_lock(d);
+ d->mem_event.req_producers--;
+ mem_event_ring_unlock(d);
+}
+
int mem_event_check_ring(struct domain *d)
{
struct vcpu *curr = current;
int free_requests;
- int ring_full;
+ int ring_full = 1;
if ( !d->mem_event.ring_page )
return -1;
@@ -165,12 +171,11 @@ int mem_event_check_ring(struct domain *
mem_event_ring_lock(d);
free_requests = RING_FREE_REQUESTS(&d->mem_event.front_ring);
- if ( unlikely(free_requests < 2) )
+ if ( d->mem_event.req_producers < free_requests )
{
- gdprintk(XENLOG_INFO, "free request slots: %d\n",
free_requests);
- WARN_ON(free_requests == 0);
+ d->mem_event.req_producers++;
+ ring_full = 0;
}
- ring_full = free_requests < MEM_EVENT_RING_THRESHOLD ? 1 : 0;
if ( (curr->domain->domain_id == d->domain_id) &&
ring_full )
{
diff -r f1349a968a5a -r b2c8dacb2dc0 xen/arch/x86/mm/mem_sharing.c
--- a/xen/arch/x86/mm/mem_sharing.c
+++ b/xen/arch/x86/mm/mem_sharing.c
@@ -281,7 +281,6 @@ static struct page_info* mem_sharing_all
vcpu_pause_nosync(v);
req.flags |= MEM_EVENT_FLAG_VCPU_PAUSED;
- /* XXX: Need to reserve a request, not just check the ring! */
if(mem_event_check_ring(d)) return page;
req.gfn = gfn;
diff -r f1349a968a5a -r b2c8dacb2dc0 xen/arch/x86/mm/p2m.c
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -803,6 +803,7 @@ void p2m_mem_paging_populate(struct doma
else if ( p2mt != p2m_ram_paging_out && p2mt != p2m_ram_paged )
{
/* gfn is already on its way back and vcpu is not paused */
+ mem_event_put_req_producers(d);
return;
}
diff -r f1349a968a5a -r b2c8dacb2dc0 xen/include/asm-x86/mem_event.h
--- a/xen/include/asm-x86/mem_event.h
+++ b/xen/include/asm-x86/mem_event.h
@@ -27,6 +27,7 @@
/* Pauses VCPU while marking pause flag for mem event */
void mem_event_mark_and_pause(struct vcpu *v);
int mem_event_check_ring(struct domain *d);
+void mem_event_put_req_producers(struct domain *d);
void mem_event_put_request(struct domain *d, mem_event_request_t *req);
void mem_event_get_response(struct domain *d, mem_event_response_t *rsp);
void mem_event_unpause_vcpus(struct domain *d);
diff -r f1349a968a5a -r b2c8dacb2dc0 xen/include/xen/sched.h
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -183,6 +183,7 @@ struct mem_event_domain
{
/* ring lock */
spinlock_t ring_lock;
+ unsigned int req_producers;
/* shared page */
mem_event_shared_page_t *shared_page;
/* shared ring page */
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