perf(cpus): make reset errata do fewer branches
Errata application is painful for performance. For a start, it's done
when the core has just come out of reset, which means branch predictors
and caches will be empty so a branch to a workaround function must be
fetched from memory and that round trip is very slow. Then it also runs
with the I-cache off, which means that the loop to iterate over the
workarounds must also be fetched from memory on each iteration.
We can remove both branches. First, we can simply apply every erratum
directly instead of defining a workaround function and jumping to it.
Currently, no errata that need to be applied at both reset and runtime,
with the same workaround function, exist. If the need arose in future,
this should be achievable with a reset + runtime wrapper combo.
Then, we can construct a function that applies each erratum linearly
instead of looping over the list. If this function is part of the reset
function, then the only "far" branches at reset will be for the checker
functions. Importantly, this mitigates the slowdown even when an erratum
is disabled.
The result is ~50% speedup on N1SDP and ~20% on AArch64 Juno on wakeup
from PSCI calls that end in powerdown. This is roughly back to the
baseline of v2.9, before the errata framework regressed on performance
(or a little better). It is important to note that there are other
slowdowns since then that remain unknown.
Change-Id: Ie4d5288a331b11fd648e5c4a0b652b74160b07b9
Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>
diff --git a/include/lib/cpus/errata.h b/include/lib/cpus/errata.h
index b9166f7..10b949f 100644
--- a/include/lib/cpus/errata.h
+++ b/include/lib/cpus/errata.h
@@ -9,20 +9,18 @@
#include <lib/cpus/cpu_ops.h>
-#define ERRATUM_WA_FUNC_SIZE CPU_WORD_SIZE
#define ERRATUM_CHECK_FUNC_SIZE CPU_WORD_SIZE
#define ERRATUM_ID_SIZE 4
#define ERRATUM_CVE_SIZE 2
#define ERRATUM_CHOSEN_SIZE 1
-#define ERRATUM_MITIGATED_SIZE 1
+#define ERRATUM_ALIGNMENT_SIZE 1
-#define ERRATUM_WA_FUNC 0
-#define ERRATUM_CHECK_FUNC ERRATUM_WA_FUNC + ERRATUM_WA_FUNC_SIZE
+#define ERRATUM_CHECK_FUNC 0
#define ERRATUM_ID ERRATUM_CHECK_FUNC + ERRATUM_CHECK_FUNC_SIZE
#define ERRATUM_CVE ERRATUM_ID + ERRATUM_ID_SIZE
#define ERRATUM_CHOSEN ERRATUM_CVE + ERRATUM_CVE_SIZE
-#define ERRATUM_MITIGATED ERRATUM_CHOSEN + ERRATUM_CHOSEN_SIZE
-#define ERRATUM_ENTRY_SIZE ERRATUM_MITIGATED + ERRATUM_MITIGATED_SIZE
+#define ERRATUM_ALIGNMENT ERRATUM_CHOSEN + ERRATUM_CHOSEN_SIZE
+#define ERRATUM_ENTRY_SIZE ERRATUM_ALIGNMENT + ERRATUM_ALIGNMENT_SIZE
/* Errata status */
#define ERRATA_NOT_APPLIES 0
@@ -39,15 +37,13 @@
* uintptr_t will reflect the change and the alignment will be correct in both.
*/
struct erratum_entry {
- uintptr_t (*wa_func)(uint64_t cpu_rev);
uintptr_t (*check_func)(uint64_t cpu_rev);
/* Will fit CVEs with up to 10 character in the ID field */
uint32_t id;
/* Denote CVEs with their year or errata with 0 */
uint16_t cve;
uint8_t chosen;
- /* TODO(errata ABI): placeholder for the mitigated field */
- uint8_t _mitigated;
+ uint8_t _alignment;
} __packed;
CASSERT(sizeof(struct erratum_entry) == ERRATUM_ENTRY_SIZE,