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make USE_NSEC work as expected
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Since the filesystem ext4 is now defined as stable in Linux v2.6.28,
and ext4 supports nanonsecond resolution timestamps natively, it is
time to make USE_NSEC work as expected.

This will make racy git situations less likely to happen.  For 'git
checkout' this means it will be less likely that we have to open, read
the contents of the file into RAM, and check if file is really
modified or not.  The result sould be a litle less used CPU time, less
pagefaults and a litle faster program, at least for 'git checkout'.

Since the number of possible racy git situations would increase when
disks gets faster, this patch would be more and more helpfull as times
go by.  For a fast Solid State Disk, this patch should be helpfull.

Note that, when file operations starts to take less than 1 nanosecond,
one would again start to get more racy git situations.

For more info on racy git, see Documentation/technical/racy-git.txt
For more info on ext4, see http://kernelnewbies.org/Ext4

Signed-off-by: Kjetil Barvik <barvik@broadpark.no>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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Kjetil Barvik authored and Junio C Hamano committed Feb 20, 2009
1 parent 8cd6192 commit fba2f38
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Showing 3 changed files with 65 additions and 19 deletions.
6 changes: 3 additions & 3 deletions cache.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -140,8 +140,8 @@ struct ondisk_cache_entry_extended {
};

struct cache_entry {
unsigned int ce_ctime;
unsigned int ce_mtime;
struct cache_time ce_ctime;
struct cache_time ce_mtime;
unsigned int ce_dev;
unsigned int ce_ino;
unsigned int ce_mode;
Expand Down Expand Up @@ -282,7 +282,7 @@ struct index_state {
struct cache_entry **cache;
unsigned int cache_nr, cache_alloc, cache_changed;
struct cache_tree *cache_tree;
time_t timestamp;
struct cache_time timestamp;
void *alloc;
unsigned name_hash_initialized : 1,
initialized : 1;
Expand Down
70 changes: 56 additions & 14 deletions read-cache.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -67,8 +67,15 @@ void rename_index_entry_at(struct index_state *istate, int nr, const char *new_n
*/
void fill_stat_cache_info(struct cache_entry *ce, struct stat *st)
{
ce->ce_ctime = st->st_ctime;
ce->ce_mtime = st->st_mtime;
ce->ce_ctime.sec = (unsigned int)st->st_ctime;
ce->ce_mtime.sec = (unsigned int)st->st_mtime;
#ifdef USE_NSEC
ce->ce_ctime.nsec = (unsigned int)st->st_ctim.tv_nsec;
ce->ce_mtime.nsec = (unsigned int)st->st_mtim.tv_nsec;
#else
ce->ce_ctime.nsec = 0;
ce->ce_mtime.nsec = 0;
#endif
ce->ce_dev = st->st_dev;
ce->ce_ino = st->st_ino;
ce->ce_uid = st->st_uid;
Expand Down Expand Up @@ -196,11 +203,18 @@ static int ce_match_stat_basic(struct cache_entry *ce, struct stat *st)
default:
die("internal error: ce_mode is %o", ce->ce_mode);
}
if (ce->ce_mtime != (unsigned int) st->st_mtime)
if (ce->ce_mtime.sec != (unsigned int)st->st_mtime)
changed |= MTIME_CHANGED;
if (trust_ctime && ce->ce_ctime != (unsigned int) st->st_ctime)
if (trust_ctime && ce->ce_ctime.sec != (unsigned int)st->st_ctime)
changed |= CTIME_CHANGED;

#ifdef USE_NSEC
if (ce->ce_mtime.nsec != (unsigned int)st->st_mtim.tv_nsec)
changed |= MTIME_CHANGED;
if (trust_ctime && ce->ce_ctime.nsec != (unsigned int)st->st_ctim.tv_nsec)
changed |= CTIME_CHANGED;
#endif

if (ce->ce_uid != (unsigned int) st->st_uid ||
ce->ce_gid != (unsigned int) st->st_gid)
changed |= OWNER_CHANGED;
Expand Down Expand Up @@ -232,8 +246,16 @@ static int ce_match_stat_basic(struct cache_entry *ce, struct stat *st)
static int is_racy_timestamp(const struct index_state *istate, struct cache_entry *ce)
{
return (!S_ISGITLINK(ce->ce_mode) &&
istate->timestamp &&
((unsigned int)istate->timestamp) <= ce->ce_mtime);
istate->timestamp.sec &&
#ifdef USE_NSEC
/* nanosecond timestamped files can also be racy! */
(istate->timestamp.sec < ce->ce_mtime.sec ||
(istate->timestamp.sec == ce->ce_mtime.sec &&
istate->timestamp.nsec <= ce->ce_mtime.nsec))
#else
istate->timestamp.sec <= ce->ce_mtime.sec
#endif
);
}

int ie_match_stat(const struct index_state *istate,
Expand Down Expand Up @@ -1159,8 +1181,15 @@ static void convert_from_disk(struct ondisk_cache_entry *ondisk, struct cache_en
size_t len;
const char *name;

ce->ce_ctime = ntohl(ondisk->ctime.sec);
ce->ce_mtime = ntohl(ondisk->mtime.sec);
ce->ce_ctime.sec = ntohl(ondisk->ctime.sec);
ce->ce_mtime.sec = ntohl(ondisk->mtime.sec);
#ifdef USE_NSEC
ce->ce_ctime.nsec = ntohl(ondisk->ctime.nsec);
ce->ce_mtime.nsec = ntohl(ondisk->mtime.nsec);
#else
ce->ce_ctime.nsec = 0;
ce->ce_mtime.nsec = 0;
#endif
ce->ce_dev = ntohl(ondisk->dev);
ce->ce_ino = ntohl(ondisk->ino);
ce->ce_mode = ntohl(ondisk->mode);
Expand Down Expand Up @@ -1226,7 +1255,8 @@ int read_index_from(struct index_state *istate, const char *path)
return istate->cache_nr;

errno = ENOENT;
istate->timestamp = 0;
istate->timestamp.sec = 0;
istate->timestamp.nsec = 0;
fd = open(path, O_RDONLY);
if (fd < 0) {
if (errno == ENOENT)
Expand Down Expand Up @@ -1278,7 +1308,13 @@ int read_index_from(struct index_state *istate, const char *path)
src_offset += ondisk_ce_size(ce);
dst_offset += ce_size(ce);
}
istate->timestamp = st.st_mtime;
istate->timestamp.sec = st.st_mtime;
#ifdef USE_NSEC
istate->timestamp.nsec = (unsigned int)st.st_mtim.tv_nsec;
#else
istate->timestamp.nsec = 0;
#endif

while (src_offset <= mmap_size - 20 - 8) {
/* After an array of active_nr index entries,
* there can be arbitrary number of extended
Expand Down Expand Up @@ -1308,14 +1344,15 @@ int read_index_from(struct index_state *istate, const char *path)

int is_index_unborn(struct index_state *istate)
{
return (!istate->cache_nr && !istate->alloc && !istate->timestamp);
return (!istate->cache_nr && !istate->alloc && !istate->timestamp.sec);
}

int discard_index(struct index_state *istate)
{
istate->cache_nr = 0;
istate->cache_changed = 0;
istate->timestamp = 0;
istate->timestamp.sec = 0;
istate->timestamp.nsec = 0;
istate->name_hash_initialized = 0;
free_hash(&istate->name_hash);
cache_tree_free(&(istate->cache_tree));
Expand Down Expand Up @@ -1461,10 +1498,15 @@ static int ce_write_entry(git_SHA_CTX *c, int fd, struct cache_entry *ce)
struct ondisk_cache_entry *ondisk = xcalloc(1, size);
char *name;

ondisk->ctime.sec = htonl(ce->ce_ctime);
ondisk->ctime.sec = htonl(ce->ce_ctime.sec);
ondisk->mtime.sec = htonl(ce->ce_mtime.sec);
#ifdef USE_NSEC
ondisk->ctime.nsec = htonl(ce->ce_ctime.nsec);
ondisk->mtime.nsec = htonl(ce->ce_mtime.nsec);
#else
ondisk->ctime.nsec = 0;
ondisk->mtime.sec = htonl(ce->ce_mtime);
ondisk->mtime.nsec = 0;
#endif
ondisk->dev = htonl(ce->ce_dev);
ondisk->ino = htonl(ce->ce_ino);
ondisk->mode = htonl(ce->ce_mode);
Expand Down
8 changes: 6 additions & 2 deletions unpack-trees.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -360,8 +360,12 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options

memset(&o->result, 0, sizeof(o->result));
o->result.initialized = 1;
if (o->src_index)
o->result.timestamp = o->src_index->timestamp;
if (o->src_index) {
o->result.timestamp.sec = o->src_index->timestamp.sec;
#ifdef USE_NSEC
o->result.timestamp.nsec = o->src_index->timestamp.nsec;
#endif
}
o->merge_size = len;

if (!dfc)
Expand Down

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