[RFC,72/86] treewide: crypto: remove cond_resched()

Commit Message

Ankur Arora Nov. 7, 2023, 11:08 p.m. UTC

There are broadly three sets of uses of cond_resched():

1.  Calls to cond_resched() out of the goodness of our heart,
    otherwise known as avoiding lockup splats.

2.  Open coded variants of cond_resched_lock() which call
    cond_resched().

3.  Retry or error handling loops, where cond_resched() is used as a
    quick alternative to spinning in a tight-loop.

When running under a full preemption model, the cond_resched() reduces
to a NOP (not even a barrier) so removing it obviously cannot matter.

But considering only voluntary preemption models (for say code that
has been mostly tested under those), for set-1 and set-2 the
scheduler can now preempt kernel tasks running beyond their time
quanta anywhere they are preemptible() [1]. Which removes any need
for these explicitly placed scheduling points.

The cond_resched() calls in set-3 are a little more difficult.
To start with, given it's NOP character under full preemption, it
never actually saved us from a tight loop.
With voluntary preemption, it's not a NOP, but it might as well be --
for most workloads the scheduler does not have an interminable supply
of runnable tasks on the runqueue.

So, cond_resched() is useful to not get softlockup splats, but not
terribly good for error handling. Ideally, these should be replaced
with some kind of timed or event wait.
For now we use cond_resched_stall(), which tries to schedule if
possible, and executes a cpu_relax() if not.

All the cond_resched() calls are from set-1. Remove them.

[1] https://lore.kernel.org/lkml/[e-mail]/

Cc: Herbert Xu <[e-mail]>
Cc: "David S. Miller" <[e-mail]>
Cc: [e-mail]
Signed-off-by: Ankur Arora <[e-mail]>
---
 crypto/internal.h |  2 +-
 crypto/tcrypt.c   |  5 -----
 crypto/testmgr.c  | 10 ----------
 3 files changed, 1 insertion(+), 16 deletions(-)

Patch

diff --git a/crypto/internal.h b/crypto/internal.h
index 63e59240d5fb..930f8f5fad39 100644
--- a/crypto/internal.h
+++ b/crypto/internal.h
@@ -203,7 +203,7 @@  static inline void crypto_notify(unsigned long val, void *v)
 static inline void crypto_yield(u32 flags)
 {
 	if (flags & CRYPTO_TFM_REQ_MAY_SLEEP)
-		cond_resched();
+		cond_resched_stall();
 }
 
 static inline int crypto_is_test_larval(struct crypto_larval *larval)
diff --git a/crypto/tcrypt.c b/crypto/tcrypt.c
index 202ca1a3105d..9f33b9724a2e 100644
--- a/crypto/tcrypt.c
+++ b/crypto/tcrypt.c
@@ -414,7 +414,6 @@  static void test_mb_aead_speed(const char *algo, int enc, int secs,
 			if (secs) {
 				ret = test_mb_aead_jiffies(data, enc, bs,
 							   secs, num_mb);
-				cond_resched();
 			} else {
 				ret = test_mb_aead_cycles(data, enc, bs,
 							  num_mb);
@@ -667,7 +666,6 @@  static void test_aead_speed(const char *algo, int enc, unsigned int secs,
 			if (secs) {
 				ret = test_aead_jiffies(req, enc, bs,
 							secs);
-				cond_resched();
 			} else {
 				ret = test_aead_cycles(req, enc, bs);
 			}
@@ -923,7 +921,6 @@  static void test_ahash_speed_common(const char *algo, unsigned int secs,
 		if (secs) {
 			ret = test_ahash_jiffies(req, speed[i].blen,
 						 speed[i].plen, output, secs);
-			cond_resched();
 		} else {
 			ret = test_ahash_cycles(req, speed[i].blen,
 						speed[i].plen, output);
@@ -1182,7 +1179,6 @@  static void test_mb_skcipher_speed(const char *algo, int enc, int secs,
 				ret = test_mb_acipher_jiffies(data, enc,
 							      bs, secs,
 							      num_mb);
-				cond_resched();
 			} else {
 				ret = test_mb_acipher_cycles(data, enc,
 							     bs, num_mb);
@@ -1397,7 +1393,6 @@  static void test_skcipher_speed(const char *algo, int enc, unsigned int secs,
 			if (secs) {
 				ret = test_acipher_jiffies(req, enc,
 							   bs, secs);
-				cond_resched();
 			} else {
 				ret = test_acipher_cycles(req, enc,
 							  bs);
diff --git a/crypto/testmgr.c b/crypto/testmgr.c
index 216878c8bc3d..2909c5aa4b8b 100644
--- a/crypto/testmgr.c
+++ b/crypto/testmgr.c
@@ -1676,7 +1676,6 @@  static int test_hash_vec(const struct hash_testvec *vec, unsigned int vec_num,
 						req, desc, tsgl, hashstate);
 			if (err)
 				return err;
-			cond_resched();
 		}
 	}
 #endif
@@ -1837,7 +1836,6 @@  static int test_hash_vs_generic_impl(const char *generic_driver,
 					req, desc, tsgl, hashstate);
 		if (err)
 			goto out;
-		cond_resched();
 	}
 	err = 0;
 out:
@@ -1966,7 +1964,6 @@  static int __alg_test_hash(const struct hash_testvec *vecs,
 		err = test_hash_vec(&vecs[i], i, req, desc, tsgl, hashstate);
 		if (err)
 			goto out;
-		cond_resched();
 	}
 	err = test_hash_vs_generic_impl(generic_driver, maxkeysize, req,
 					desc, tsgl, hashstate);
@@ -2246,7 +2243,6 @@  static int test_aead_vec(int enc, const struct aead_testvec *vec,
 						&cfg, req, tsgls);
 			if (err)
 				return err;
-			cond_resched();
 		}
 	}
 #endif
@@ -2476,7 +2472,6 @@  static int test_aead_inauthentic_inputs(struct aead_extra_tests_ctx *ctx)
 			if (err)
 				return err;
 		}
-		cond_resched();
 	}
 	return 0;
 }
@@ -2580,7 +2575,6 @@  static int test_aead_vs_generic_impl(struct aead_extra_tests_ctx *ctx)
 			if (err)
 				goto out;
 		}
-		cond_resched();
 	}
 	err = 0;
 out:
@@ -2659,7 +2653,6 @@  static int test_aead(int enc, const struct aead_test_suite *suite,
 		err = test_aead_vec(enc, &suite->vecs[i], i, req, tsgls);
 		if (err)
 			return err;
-		cond_resched();
 	}
 	return 0;
 }
@@ -3006,7 +2999,6 @@  static int test_skcipher_vec(int enc, const struct cipher_testvec *vec,
 						    &cfg, req, tsgls);
 			if (err)
 				return err;
-			cond_resched();
 		}
 	}
 #endif
@@ -3203,7 +3195,6 @@  static int test_skcipher_vs_generic_impl(const char *generic_driver,
 					    cfg, req, tsgls);
 		if (err)
 			goto out;
-		cond_resched();
 	}
 	err = 0;
 out:
@@ -3236,7 +3227,6 @@  static int test_skcipher(int enc, const struct cipher_test_suite *suite,
 		err = test_skcipher_vec(enc, &suite->vecs[i], i, req, tsgls);
 		if (err)
 			return err;
-		cond_resched();
 	}
 	return 0;
 }