On 05.08.20 12:32, Julien Grall wrote:
Hi Julien
@@ -2275,6 +2282,16 @@ static void check_for_vcpu_work(void)
*/
void leave_hypervisor_to_guest(void)
{
+#ifdef CONFIG_IOREQ_SERVER
+ /*
+ * XXX: Check the return. Shall we call that in
+ * continue_running and context_switch instead?
+ * The benefits would be to avoid calling
+ * handle_hvm_io_completion on every return.
+ */
Yeah, that could be a simple and good optimization
Well, it is not simple as it is sounds :). handle_hvm_io_completion()
is the function in charge to mark the vCPU as waiting for I/O. So we
would at least need to split the function.
I wrote this TODO because I wasn't sure about the complexity of
handle_hvm_io_completion(current). Looking at it again, the main
complexity is the looping over the IOREQ servers.
I think it would be better to optimize handle_hvm_io_completion()
rather than trying to hack the context_switch() or continue_running().
Well, is the idea in proposed dirty test patch below close to what you
expect? Patch optimizes handle_hvm_io_completion() to avoid extra
actions if vcpu's domain doesn't have ioreq_server, alternatively
the check could be moved out of handle_hvm_io_completion() to avoid
calling that function at all. BTW, TODO also suggests checking the
return value of handle_hvm_io_completion(), but I am completely sure we
can simply
just return from leave_hypervisor_to_guest() at this point. Could you
please share your opinion?
---
xen/common/hvm/ioreq.c | 12 +++++++++++-
xen/include/asm-arm/domain.h | 1 +
xen/include/xen/hvm/ioreq.h | 5 +++++
3 files changed, 17 insertions(+), 1 deletion(-)
diff --git a/xen/common/hvm/ioreq.c b/xen/common/hvm/ioreq.c
index 7e1fa23..dc6647a 100644
--- a/xen/common/hvm/ioreq.c
+++ b/xen/common/hvm/ioreq.c
@@ -38,9 +38,15 @@ static void set_ioreq_server(struct domain *d,
unsigned int id,
struct hvm_ioreq_server *s)
{
ASSERT(id < MAX_NR_IOREQ_SERVERS);
- ASSERT(!s || !d->arch.hvm.ioreq_server.server[id]);
+ ASSERT((!s && d->arch.hvm.ioreq_server.server[id]) ||
+ (s && !d->arch.hvm.ioreq_server.server[id]));
d->arch.hvm.ioreq_server.server[id] = s;
+
+ if ( s )
+ d->arch.hvm.ioreq_server.nr_servers ++;
+ else
+ d->arch.hvm.ioreq_server.nr_servers --;
}
/*
@@ -169,6 +175,9 @@ bool handle_hvm_io_completion(struct vcpu *v)
return false;
}
+ if ( !hvm_domain_has_ioreq_server(d) )
+ return true;
+
FOR_EACH_IOREQ_SERVER(d, id, s)
{
struct hvm_ioreq_vcpu *sv;
@@ -1415,6 +1424,7 @@ unsigned int hvm_broadcast_ioreq(ioreq_t *p, bool
buffered)
void hvm_ioreq_init(struct domain *d)
{
spin_lock_init(&d->arch.hvm.ioreq_server.lock);
+ d->arch.hvm.ioreq_server.nr_servers = 0;
arch_hvm_ioreq_init(d);
}
diff --git a/xen/include/asm-arm/domain.h b/xen/include/asm-arm/domain.h
index 6a01d69..484bd1a 100644
--- a/xen/include/asm-arm/domain.h
+++ b/xen/include/asm-arm/domain.h
@@ -68,6 +68,7 @@ struct hvm_domain
struct {
spinlock_t lock;
struct hvm_ioreq_server *server[MAX_NR_IOREQ_SERVERS];
+ unsigned int nr_servers;
} ioreq_server;
bool_t qemu_mapcache_invalidate;
diff --git a/xen/include/xen/hvm/ioreq.h b/xen/include/xen/hvm/ioreq.h
index 40b7b5e..8f78852 100644
--- a/xen/include/xen/hvm/ioreq.h
+++ b/xen/include/xen/hvm/ioreq.h
@@ -23,6 +23,11 @@
#include <asm/hvm/ioreq.h>
+static inline bool hvm_domain_has_ioreq_server(const struct domain *d)
+{
+ return (d->arch.hvm.ioreq_server.nr_servers > 0);
+}
+
#define GET_IOREQ_SERVER(d, id) \
(d)->arch.hvm.ioreq_server.server[id]
--
2.7.4
--
Regards,
Oleksandr Tyshchenko
