Hello, Marco,
On Thu, Aug 26, 2021 at 11:36 AM Marco Elver elver@google.com wrote:
On Thu, 26 Aug 2021 at 03:26, 'Isabella Basso' via KUnit Development kunit-dev@googlegroups.com wrote:
Keep function signatures minimal by making common definitions static. This does not change any behavior.
This seems like an odd change; if I read it right it's changing the out-param passed to test_int_hash() to simply be static globals.
For one, it makes the code harder to read because now test_int_hash() is no longer "pure" (no global side-effects ... modulo printfs), and what was previously an out-param, is now a global.
Unfortunately this is poor style and likely to lead to hard-to-debug problems. One such problem is if suddenly you have multiple threads involved. While this is just a test and unlikely to be a problem, I would recommend not introducing global state carelessly.
I see. My peers at LKCamp and I talked over the thread-safety problems for a while but we concluded it wasn't a big deal (precisely because this is a test). Though being stylistically poor seems a huge heads up, so I'm really thankful for your thorough explanation(, and review)! Noted! :)
An alternative common idiom, where a set of variables are always passed around to other functions, is to introduce a struct and pass a pointer to it along.
Signed-off-by: Isabella Basso isabellabdoamaral@usp.br
lib/test_hash.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-)
diff --git a/lib/test_hash.c b/lib/test_hash.c index d4b0cfdb0377..8bcc645a7294 100644 --- a/lib/test_hash.c +++ b/lib/test_hash.c @@ -23,6 +23,11 @@ #include <linux/stringhash.h> #include <linux/printk.h>
+#define SIZE 256 /* Run time is cubic in SIZE */
+static u32 string_or; /* stores or-ed string output */ +static u32 hash_or[2][33] = { { 0, } }; /* stores or-ed hash output */
These now use up memory for as long as this module is loaded, vs. before where it would only use up stack space. (For a test that's not a problem, but in non-test code it might.)
/* 32-bit XORSHIFT generator. Seed must not be zero. */ static u32 __init __attribute_const__ xorshift(u32 seed) @@ -66,7 +71,7 @@ fill_buf(char *buf, size_t len, u32 seed)
- recompile and re-test the module without rebooting.
*/ static bool __init -test_int_hash(unsigned long long h64, u32 hash_or[2][33]) +test_int_hash(unsigned long long h64) { int k; u32 h0 = (u32)h64, h1, h2; @@ -123,17 +128,15 @@ test_int_hash(unsigned long long h64, u32 hash_or[2][33]) return true; }
-#define SIZE 256 /* Run time is cubic in SIZE */
static int __init test_hash_init(void) { char buf[SIZE+1];
u32 string_or = 0, hash_or[2][33] = { { 0, } }; unsigned tests = 0; unsigned long long h64 = 0; int i, j;
string_or = 0;That's another problem with changes like this; now the compiler has no chance to warn you in case the variable is not initialized correctly.
Also, I don't see string_or used anywhere else. Why make it global? If a later change would require that, it should say so in the commit message. But my guess is you can avoid all that by bundling everything up in a struct.
fill_buf(buf, SIZE, 1); /* Test every possible non-empty substring in the buffer. */@@ -161,7 +164,7 @@ test_hash_init(void)
string_or |= h0; h64 = h64 << 32 | h0; /* For use with hash_64 */
if (!test_int_hash(h64, hash_or))
if (!test_int_hash(h64)) return -EINVAL; tests++; } /* i */-- 2.33.0
Thanks, -- Isabella Basso