| Message ID | 20220823095733.58685-1-szeder.dev@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | c4bbd9bb8fd307c3c8be16121391416a5685ffe1 |
| Headers | show |
| Series | [v2] promisor-remote: fix xcalloc() argument order | expand |
On Tue, Aug 23, 2022 at 11:57:33AM +0200, SZEDER Gábor wrote: > Pass the number of elements first and their size second, as expected > by xcalloc(). > > Patch generated with: > > make SPATCH_FLAGS=--recursive-includes contrib/coccinelle/xcalloc.cocci.patch Thanks for digging here. I think it probably explains a lot of "wait, why did this result change" head-scratching I did back when we started batching a few years ago. Is there any reason we wouldn't want --recursive-includes to be added to the default SPATCH_FLAGS? I suspect we'd still want to leave --all-includes there to get as much type information as possible. If I understand correctly, the two are orthogonal (one is "follow includes of includes" and the other is "follow system includes in angle brackets"). Doing so doesn't seem to find any other missed entries in the current codebase, but I'm pretty sure there are some it would have caught in a less mysterious fashion over the years. -Peff
On Wed, Aug 24, 2022 at 04:32:41AM -0400, Jeff King wrote: > On Tue, Aug 23, 2022 at 11:57:33AM +0200, SZEDER Gábor wrote: > > > Pass the number of elements first and their size second, as expected > > by xcalloc(). > > > > Patch generated with: > > > > make SPATCH_FLAGS=--recursive-includes contrib/coccinelle/xcalloc.cocci.patch > > Thanks for digging here. I think it probably explains a lot of "wait, > why did this result change" head-scratching I did back when we started > batching a few years ago. > > Is there any reason we wouldn't want --recursive-includes to be added to > the default SPATCH_FLAGS? I ran some runtime measurements yesterday, and there is a considerable runtime increase in the unbatched case: The tables below show the runtimes of applying each of our semantic patches separately with Coccinelle v1.1.1, with the '--all-includes' or '--recursive-includes' flags and with batch sizes 1 (no batching) or 32, i.e.: time make SPATCH_FLAGS=$flag SPATCH_BATCH_SIZE=$size $cocci.patch SPATCH_BATCH_SIZE=1: semantic patch | all | recursive | -----------------+-----------+-----------+-------- array | 69.90s | 140.12s | +100% commit | 94.44s | 223.63s | +137% equals-null | 86.93s | 205.40s | +136% flex_alloc | 11.32s | 16.45s | +45% free | 70.47s | 159.75s | +127% hashmap | 83.48s | 199.70s | +139% object_id | 107.83s | 241.69s | +124% preincr | 79.33s | 202.98s | +156% qsort | 16.20s | 33.86s | +109% strbuf | 60.54s | 129.93s | +115% swap | 81.70s | 200.75s | +146% unused | 499.19s | 626.35s | +25% xcalloc | 26.71s | 57.63s | +116% xopen | 30.92s | 59.26s | +92% xstrdup_or_null | 5.05s | 6.94s | +37% -----------------+-----------+-----------+-------- all | 1324s | 2504s | +89% SPATCH_BATCH_SIZE=32: semantic patch | all | recursive | -----------------+-----------+-----------+-------- array | 43.81s | 52.83s | +21% commit | 50.16s | 52.76s | +5% equals-null | 47.77s | 50.86s | +6% flex_alloc | 41.00s | 43.64s | +6% free | 43.12s | 46.68s | +8% hashmap | 42.76s | 46.12s | +8% object_id | 56.17s | 60.00s | +7% preincr | 39.82s | 42.57s | +7% qsort | 39.48s | 53.09s | +34% strbuf | 51.27s | 49.38s | -4% swap | 41.93s | 58.17s | +39% unused | 440.86s | 445.47s | +1% xcalloc | 39.90s | 42.22s | +6% xopen | 40.26s | 43.19s | +7% xstrdup_or_null | 39.14s | 41.72s | +7% -----------------+-----------+-----------+-------- all | 1057s | 1129s | +7% I don't have meaningful numbers about the impact of '--recursive-includes' on the runtime of a parallel 'make -j<N> coccicheck', because they're severely skewed by 'unused.cocci' and 'make's scheduler: applying 'unused.cocci' takes 5-10x as long as other semantic patches (accounting for about 38-42% of the total sequential runtime), and 'make' on my system usually schedules it near the end, meaning that for a significant part there is no parallel processing at all. So I'm not sure about making '--recursive-includes' the default, at least as long as we don't batch by default. However, we could still use this flag in CI... > I suspect we'd still want to leave --all-includes there to get as much > type information as possible. If I understand correctly, the two are > orthogonal (one is "follow includes of includes" and the other is > "follow system includes in angle brackets"). 'spatch --help' tells me: --recursive-includes causes all available include files, both those included in the C file(s) and those included in header files, to be used --all-includes causes all available include files included in the C file(s) to be used So I think the difference is not about system includes, but rather about "consider includes of includes" vs. "consider only direct includes in the C files", so it seems '--recursive-includes' is a superset of '--all-includes'. Oh, and let's not forget the rather surprising behavior that if spatch processes multiple C files at once, then for each of the C files it considers all includes from all C files; this explains why '--all-includes promisor-remote.c config.c' works, because 'config.c' does include 'repository.h', supplying the necessary type information to catch the previously missed transformation in 'promisor-remote.c'. These descriptions don't make it clear (to me) whether the two options are orthogonal, exclusive, or something else. However, trying out various combinations indicates that "last one wins", e.g.: $ spatch --recursive-includes --all-includes --sp-file contrib/coccinelle/xcalloc.cocci --patch . promisor-remote.c warning: Can't find macro file: /usr/local/bin/lib/coccinelle/standard.h warning: Can't find default iso file: /usr/local/bin/lib/coccinelle/standard.iso HANDLING: promisor-remote.c $ spatch --all-includes --recursive-includes --sp-file contrib/coccinelle/xcalloc.cocci --patch . promisor-remote.c warning: Can't find macro file: /usr/local/bin/lib/coccinelle/standard.h warning: Can't find default iso file: /usr/local/bin/lib/coccinelle/standard.iso HANDLING: promisor-remote.c diff = diff -u -p a/promisor-remote.c b/promisor-remote.c --- a/promisor-remote.c +++ b/promisor-remote.c @@ -146,7 +146,7 @@ static void promisor_remote_init(struct if (r->promisor_remote_config) return; config = r->promisor_remote_config = - xcalloc(sizeof(*r->promisor_remote_config), 1); + xcalloc(1, sizeof(*r->promisor_remote_config)); config->promisors_tail = &config->promisors; repo_config(r, promisor_remote_config, config);
SZEDER Gábor <szeder.dev@gmail.com> writes: > Patch generated with: > > make SPATCH_FLAGS=--recursive-includes contrib/coccinelle/xcalloc.cocci.patch > > Our default SPATCH_FLAGS ('--all-includes') doesn't catch this > transformation by default, unless used in combination with a large-ish > SPATCH_BATCH_SIZE which happens to put 'promisor-remote.c' with a file > that includes 'repository.h' directly in the same batch. Our default SPATCH_FLAGS is actually SPATCH_FLAGS = --all-includes --patch . and I am wondering how "--patch ." part (or droppage thereof due to overriding it from the command line) affects the outcome. In any case, good finding how the header file inclusion was affected with batch-size and this option that solved a mystery. Thanks.
On Wed, Aug 24, 2022 at 08:58:21AM -0700, Junio C Hamano wrote: > SZEDER Gábor <szeder.dev@gmail.com> writes: > > > Patch generated with: > > > > make SPATCH_FLAGS=--recursive-includes contrib/coccinelle/xcalloc.cocci.patch > > > > Our default SPATCH_FLAGS ('--all-includes') doesn't catch this > > transformation by default, unless used in combination with a large-ish > > SPATCH_BATCH_SIZE which happens to put 'promisor-remote.c' with a file > > that includes 'repository.h' directly in the same batch. > > Our default SPATCH_FLAGS is actually > > SPATCH_FLAGS = --all-includes --patch . > > and I am wondering how "--patch ." part (or droppage thereof due to > overriding it from the command line) affects the outcome. '--patch .' is not part of SPATCH_FLAGS anymore, and for a good reason, see the recent 7b63ea5750 (Makefile: remove mandatory "spatch" arguments from SPATCH_FLAGS, 2022-07-05).
SZEDER Gábor <szeder.dev@gmail.com> writes: > On Wed, Aug 24, 2022 at 08:58:21AM -0700, Junio C Hamano wrote: >> SZEDER Gábor <szeder.dev@gmail.com> writes: >> >> > Patch generated with: >> > >> > make SPATCH_FLAGS=--recursive-includes contrib/coccinelle/xcalloc.cocci.patch >> > >> > Our default SPATCH_FLAGS ('--all-includes') doesn't catch this >> > transformation by default, unless used in combination with a large-ish >> > SPATCH_BATCH_SIZE which happens to put 'promisor-remote.c' with a file >> > that includes 'repository.h' directly in the same batch. >> >> Our default SPATCH_FLAGS is actually >> >> SPATCH_FLAGS = --all-includes --patch . >> >> and I am wondering how "--patch ." part (or droppage thereof due to >> overriding it from the command line) affects the outcome. > > '--patch .' is not part of SPATCH_FLAGS anymore, and for a good > reason, see the recent 7b63ea5750 (Makefile: remove mandatory "spatch" > arguments from SPATCH_FLAGS, 2022-07-05). Ahh, that makes my life a bit more cumbersome, as I was looking at how we did things on the 'maint' branch. Thanks, mystery solved.
On Wed, Aug 24, 2022 at 01:39:01PM +0200, SZEDER Gábor wrote: > I ran some runtime measurements yesterday, and there is a considerable > runtime increase in the unbatched case: Let me condense and rearrange this a bit to the part I think is important: > semantic patch | all | recursive | > -----------------+-----------+-----------+-------- > SPATCH_BATCH_SIZE=1: > all | 1324s | 2504s | +89% > SPATCH_BATCH_SIZE=32: > all | 1057s | 1129s | +7% Right, that's not surprising. "recursive" means we're looking at more header files than before. For the batch case it has less impact because it's more likely that some other file we're processing in the batch _also_ was looking at that header, so we saw it anyway. With an infinite bath size, adding --recursive-includes should make no difference (or almost none; it's possible there are headers which are _only_ included recursively across the whole code base). My numbers for array.cocci are: SPATCH_BATCH_SIZE=1, 133s SPATCH_BATCH_SIZE=32, 34s SPATCH_BATCH_SIZE=0, 31s Of course there we run into potential memory problems. Based on glancing at top occasionally, the first one peaked around 100MB of memory, the second around 200MB, and the third one around 2GB. So "32" is probably still a reasonable middle ground for CPU vs memory. Spending extra CPU, especially for people stuck BATCH_SIZE=1, does suck. But the tool is already terribly slow. Even if we spend twice as much CPU (which is what your numbers above show), isn't it worth it to get the _correct_ result? To me there is not much point in running it at all if it misses cases. It would be nice if there was some way to tell coccinelle not to actually _analyze_ included header files, but just to include them to pick up types, etc (and then we'd add the headers themselves to COCCI_SOURCES to check them). But I don't see a way to do that. And I wouldn't be surprised if the code simply isn't written in a way to make that easy internally. Another alternative would be --no-includes (and again, listing the headers manually via COCCI_SOURCES). But as the example you found shows, it really does need the headers in order to properly process the code in the C files themselves. > I don't have meaningful numbers about the impact of > '--recursive-includes' on the runtime of a parallel 'make -j<N> > coccicheck', because they're severely skewed by 'unused.cocci' and > 'make's scheduler: applying 'unused.cocci' takes 5-10x as long as > other semantic patches (accounting for about 38-42% of the total > sequential runtime), and 'make' on my system usually schedules it near > the end, meaning that for a significant part there is no parallel > processing at all. It may be that unused.cocci can be optimized. Once upon a time I spent some effort optimizing some of the rules files. I found that if you relied on having python support, it helped quite a bit, because without it you are stuck with the "..." operator, which can be very expensive. More details in this thread: https://lore.kernel.org/git/20180824064228.GA3183@sigill.intra.peff.net/ Back then the debian package wasn't being actively updated, and it wasn't clear if python support would remain. But these days it seems a bit more stable. And with the CI job available, I'd prefer to optimize over making the tool pleasant to use for people who do use it, rather than worrying that everybody on every platform/build can use it. All that said, I am not about to get sucked into the rabbit hole of coccinelle optimization anytime soon. So good luck to you, if you're interested. ;) > > I suspect we'd still want to leave --all-includes there to get as much > > type information as possible. If I understand correctly, the two are > > orthogonal (one is "follow includes of includes" and the other is > > "follow system includes in angle brackets"). > > 'spatch --help' tells me: > > --recursive-includes causes all available include files, both > those included in the C file(s) and those > included in header files, to be used > --all-includes causes all available include files included > in the C file(s) to be used > > So I think the difference is not about system includes, but rather > about "consider includes of includes" vs. "consider only direct > includes in the C files", so it seems '--recursive-includes' is a > superset of '--all-includes'. I'm not sure, because there's also --local-includes and --no-includes, which are grouped with --all-includes. (The grouping is doubly confusing because my copy of the manpage has _two_ options sections, and only some of the options are mentioned together in the first one). > Oh, and let's not forget the rather surprising behavior that if spatch > processes multiple C files at once, then for each of the C files it > considers all includes from all C files; this explains why > '--all-includes promisor-remote.c config.c' works, because 'config.c' > does include 'repository.h', supplying the necessary type information > to catch the previously missed transformation in 'promisor-remote.c'. Right. I have a feeling it is sucking in as much data as possible to a global symbol table, and then doing the analysis. At least that's how I'd implement it. ;) > These descriptions don't make it clear (to me) whether the two options > are orthogonal, exclusive, or something else. However, trying out various > combinations indicates that "last one wins", e.g.: OK, that's compelling evidence. In that case it wouldn't hurt to say: --all-includes --recursive-includes versus just --recursive-includes but it also probably isn't doing anything. ;) -Peff
On Wed, Aug 24 2022, Jeff King wrote: > On Tue, Aug 23, 2022 at 11:57:33AM +0200, SZEDER Gábor wrote: > >> Pass the number of elements first and their size second, as expected >> by xcalloc(). >> >> Patch generated with: >> >> make SPATCH_FLAGS=--recursive-includes contrib/coccinelle/xcalloc.cocci.patch > > Thanks for digging here. I think it probably explains a lot of "wait, > why did this result change" head-scratching I did back when we started > batching a few years ago. > > Is there any reason we wouldn't want --recursive-includes to be added to > the default SPATCH_FLAGS? > > I suspect we'd still want to leave --all-includes there to get as much > type information as possible. If I understand correctly, the two are > orthogonal (one is "follow includes of includes" and the other is > "follow system includes in angle brackets"). > > Doing so doesn't seem to find any other missed entries in the current > codebase, but I'm pretty sure there are some it would have caught in a > less mysterious fashion over the years. This feels to me like hacks around other issues we should fix the root cause of. So, first of all, I think this is a perfectly good fix, and something we should do more of in general. It'll apply the wanted change *and* speed up the run: diff --git a/contrib/coccinelle/xcalloc.cocci b/contrib/coccinelle/xcalloc.cocci index c291011607e..bd51e33af83 100644 --- a/contrib/coccinelle/xcalloc.cocci +++ b/contrib/coccinelle/xcalloc.cocci @@ -1,10 +1,8 @@ @@ -type T; -T *ptr; expression n; @@ xcalloc( + n, - \( sizeof(T) \| sizeof(*ptr) \) + sizeof(...) - , n ) But it's *not* functionally the same thing, pedantically speaking, but I think it's fine. I pointed this out at the the time in [1]. Also, more generally we could avoid includes in headers, and use forward decls. This would make e.g. the "iwyu" tool report the missing include. Unfortunately it seems we added it in this case due to "the_repository". I wonder if this hack would be better: diff --git a/Makefile b/Makefile index 9410a587fc0..92d5726b392 100644 --- a/Makefile +++ b/Makefile @@ -3119,6 +3119,7 @@ HCC = $(HCO:hco=hcc) %.hcc: %.h @echo '#include "git-compat-util.h"' >$@ + @echo "extern struct repository *the_repository;" >>$@ @echo '#include "$<"' >>$@ $(HCO): %.hco: %.hcc FORCE diff --git a/promisor-remote.h b/promisor-remote.h index edc45ab0f5f..e864c093a44 100644 --- a/promisor-remote.h +++ b/promisor-remote.h @@ -1,7 +1,7 @@ #ifndef PROMISOR_REMOTE_H #define PROMISOR_REMOTE_H -#include "repository.h" +struct repository; struct object_id; @@ -23,6 +23,7 @@ static inline void promisor_remote_reinit(void) repo_promisor_remote_reinit(the_repository); } +struct promisor_remote_config; void promisor_remote_clear(struct promisor_remote_config *config); struct promisor_remote *repo_promisor_remote_find(struct repository *r, const char *remote_name); So yeah, one way to deal with this is --recursive-includes, but I think we're better off heading in the direction of having the includes for a given *.c file be what it actually needs, and not rely on includes by proxy, or in this case to pollute the namespace of everyone using promisor-remote.h with remote.h (probably doesn't matter in that case, but in the general case...). 1. https://lore.kernel.org/git/87ft18tcog.fsf@evledraar.gmail.com/
diff --git a/promisor-remote.c b/promisor-remote.c index 5b33f88bca..68f46f5ec7 100644 --- a/promisor-remote.c +++ b/promisor-remote.c @@ -146,7 +146,7 @@ static void promisor_remote_init(struct repository *r) if (r->promisor_remote_config) return; config = r->promisor_remote_config = - xcalloc(sizeof(*r->promisor_remote_config), 1); + xcalloc(1, sizeof(*r->promisor_remote_config)); config->promisors_tail = &config->promisors; repo_config(r, promisor_remote_config, config);
Pass the number of elements first and their size second, as expected by xcalloc(). Patch generated with: make SPATCH_FLAGS=--recursive-includes contrib/coccinelle/xcalloc.cocci.patch Our default SPATCH_FLAGS ('--all-includes') doesn't catch this transformation by default, unless used in combination with a large-ish SPATCH_BATCH_SIZE which happens to put 'promisor-remote.c' with a file that includes 'repository.h' directly in the same batch. Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com> --- promisor-remote.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)