[PATCH v2 01/18] x86/sgx: Call cond_resched() at the end of sgx_reclaim_pages()

From: Kristen Carlson Accardi
Date: Fri Dec 02 2022 - 13:37:13 EST


From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>

In order to avoid repetition of cond_resched() in ksgxd() and
sgx_alloc_epc_page(), move the invocation of post-reclaim cond_resched()
inside sgx_reclaim_pages(). Except in the case of sgx_reclaim_direct(),
sgx_reclaim_pages() is always called in a loop and is always followed
by a call to cond_resched(). This will hold true for the EPC cgroup
as well, which adds even more calls to sgx_reclaim_pages() and thus
cond_resched(). Calls to sgx_reclaim_direct() may be performance
sensitive. Allow sgx_reclaim_direct() to avoid the cond_resched()
call by moving the original sgx_reclaim_pages() call to
__sgx_reclaim_pages() and then have sgx_reclaim_pages() become a
wrapper around that call with a cond_resched().

Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Signed-off-by: Kristen Carlson Accardi <kristen@xxxxxxxxxxxxxxx>
Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kernel/cpu/sgx/main.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 160c8dbee0ab..ffce6fc70a1f 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -287,7 +287,7 @@ static void sgx_reclaimer_write(struct sgx_epc_page *epc_page,
* problematic as it would increase the lock contention too much, which would
* halt forward progress.
*/
-static void sgx_reclaim_pages(void)
+static void __sgx_reclaim_pages(void)
{
struct sgx_epc_page *chunk[SGX_NR_TO_SCAN];
struct sgx_backing backing[SGX_NR_TO_SCAN];
@@ -369,6 +369,12 @@ static void sgx_reclaim_pages(void)
}
}

+static void sgx_reclaim_pages(void)
+{
+ __sgx_reclaim_pages();
+ cond_resched();
+}
+
static bool sgx_should_reclaim(unsigned long watermark)
{
return atomic_long_read(&sgx_nr_free_pages) < watermark &&
@@ -378,12 +384,14 @@ static bool sgx_should_reclaim(unsigned long watermark)
/*
* sgx_reclaim_direct() should be called (without enclave's mutex held)
* in locations where SGX memory resources might be low and might be
- * needed in order to make forward progress.
+ * needed in order to make forward progress. This call to
+ * __sgx_reclaim_pages() avoids the cond_resched() in sgx_reclaim_pages()
+ * to improve performance.
*/
void sgx_reclaim_direct(void)
{
if (sgx_should_reclaim(SGX_NR_LOW_PAGES))
- sgx_reclaim_pages();
+ __sgx_reclaim_pages();
}

static int ksgxd(void *p)
@@ -410,8 +418,6 @@ static int ksgxd(void *p)

if (sgx_should_reclaim(SGX_NR_HIGH_PAGES))
sgx_reclaim_pages();
-
- cond_resched();
}

return 0;
@@ -582,7 +588,6 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim)
}

sgx_reclaim_pages();
- cond_resched();
}

if (sgx_should_reclaim(SGX_NR_LOW_PAGES))
--
2.38.1