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Subject[PATCH v3 3/8] KVM: selftests: Add configurable demand paging delay
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When running the demand paging test with the -u option, the User Fault
FD handler essentially adds an arbitrary delay to page fault resolution.
To enable better simulation of a real demand paging scenario, add a
configurable delay to the UFFD handler.

Signed-off-by: Ben Gardon <bgardon@google.com>
---
.../selftests/kvm/demand_paging_test.c | 32 +++++++++++++++----
1 file changed, 25 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/kvm/demand_paging_test.c b/tools/testing/selftests/kvm/demand_paging_test.c
index a8f775dab7d4a..11de5b58995fb 100644
--- a/tools/testing/selftests/kvm/demand_paging_test.c
+++ b/tools/testing/selftests/kvm/demand_paging_test.c
@@ -142,12 +142,14 @@ bool quit_uffd_thread;

struct uffd_handler_args {
int uffd;
+ useconds_t delay;
};

static void *uffd_handler_thread_fn(void *arg)
{
struct uffd_handler_args *uffd_args = (struct uffd_handler_args *)arg;
int uffd = uffd_args->uffd;
+ useconds_t delay = uffd_args->delay;
int64_t pages = 0;

while (!quit_uffd_thread) {
@@ -203,6 +205,8 @@ static void *uffd_handler_thread_fn(void *arg)
if (!(msg.event & UFFD_EVENT_PAGEFAULT))
continue;

+ if (delay)
+ usleep(delay);
addr = msg.arg.pagefault.address;
r = handle_uffd_page_request(uffd, addr);
if (r < 0)
@@ -214,7 +218,8 @@ static void *uffd_handler_thread_fn(void *arg)
}

static int setup_demand_paging(struct kvm_vm *vm,
- pthread_t *uffd_handler_thread)
+ pthread_t *uffd_handler_thread,
+ useconds_t uffd_delay)
{
int uffd;
struct uffdio_api uffdio_api;
@@ -252,6 +257,7 @@ static int setup_demand_paging(struct kvm_vm *vm,
}

uffd_args.uffd = uffd;
+ uffd_args.delay = uffd_delay;
pthread_create(uffd_handler_thread, NULL, uffd_handler_thread_fn,
&uffd_args);

@@ -261,7 +267,8 @@ static int setup_demand_paging(struct kvm_vm *vm,
#define GUEST_MEM_SHIFT 30 /* 1G */
#define PAGE_SHIFT_4K 12

-static void run_test(enum vm_guest_mode mode, bool use_uffd)
+static void run_test(enum vm_guest_mode mode, bool use_uffd,
+ useconds_t uffd_delay)
{
pthread_t vcpu_thread;
pthread_t uffd_handler_thread;
@@ -326,7 +333,8 @@ static void run_test(enum vm_guest_mode mode, bool use_uffd)
if (use_uffd) {
/* Set up user fault fd to handle demand paging requests. */
quit_uffd_thread = false;
- r = setup_demand_paging(vm, &uffd_handler_thread);
+ r = setup_demand_paging(vm, &uffd_handler_thread,
+ uffd_delay);
if (r < 0)
exit(-r);
}
@@ -373,7 +381,7 @@ static void help(char *name)
int i;

puts("");
- printf("usage: %s [-h] [-m mode] [-u]\n", name);
+ printf("usage: %s [-h] [-m mode] [-u] [-d uffd_delay_usec]\n", name);
printf(" -m: specify the guest mode ID to test\n"
" (default: test all supported modes)\n"
" This option may be used multiple times.\n"
@@ -382,7 +390,11 @@ static void help(char *name)
printf(" %d: %s%s\n", i, vm_guest_mode_string(i),
vm_guest_mode_params[i].supported ? " (supported)" : "");
}
- printf(" -u: Use User Fault FD to handle vCPU page faults.\n");
+ printf(" -u: use User Fault FD to handle vCPU page\n"
+ " faults.\n");
+ printf(" -d: add a delay in usec to the User Fault\n"
+ " FD handler to simulate demand paging\n"
+ " overheads. Ignored without -u.\n");
puts("");
exit(0);
}
@@ -393,6 +405,7 @@ int main(int argc, char *argv[])
unsigned int mode;
int opt, i;
bool use_uffd = false;
+ useconds_t uffd_delay = 0;

#ifdef __x86_64__
vm_guest_mode_params_init(VM_MODE_PXXV48_4K, true, true);
@@ -401,7 +414,7 @@ int main(int argc, char *argv[])
vm_guest_mode_params_init(VM_MODE_P40V48_4K, true, true);
#endif

- while ((opt = getopt(argc, argv, "hm:u")) != -1) {
+ while ((opt = getopt(argc, argv, "hm:ud:")) != -1) {
switch (opt) {
case 'm':
if (!mode_selected) {
@@ -417,6 +430,11 @@ int main(int argc, char *argv[])
case 'u':
use_uffd = true;
break;
+ case 'd':
+ uffd_delay = strtoul(optarg, NULL, 0);
+ TEST_ASSERT(uffd_delay >= 0,
+ "A negative UFFD delay is not supported.");
+ break;
case 'h':
default:
help(argv[0]);
@@ -430,7 +448,7 @@ int main(int argc, char *argv[])
TEST_ASSERT(vm_guest_mode_params[i].supported,
"Guest mode ID %d (%s) not supported.",
i, vm_guest_mode_string(i));
- run_test(i, use_uffd);
+ run_test(i, use_uffd, uffd_delay);
}

return 0;
--
2.24.1.735.g03f4e72817-goog
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