| Message ID | 20210826012626.1163705-3-isabellabdoamaral@usp.br (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | test_hash.c: refactor into KUnit | expand |
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. 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 > > -- > You received this message because you are subscribed to the Google Groups "KUnit Development" group. > To unsubscribe from this group and stop receiving emails from it, send an email to kunit-dev+unsubscribe@googlegroups.com. > To view this discussion on the web visit https://groups.google.com/d/msgid/kunit-dev/20210826012626.1163705-3-isabellabdoamaral%40usp.br.
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
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 */ + /* 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; 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 */
Keep function signatures minimal by making common definitions static. This does not change any behavior. Signed-off-by: Isabella Basso <isabellabdoamaral@usp.br> --- lib/test_hash.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-)