Re: [PATCH v3] statx: optimize copy of struct statx to userspace
Hi David, On Sun, Mar 12, 2017 at 09:11:53AM +, David Howells wrote: > Eric Biggerswrote: > > > +static int cp_statx(const struct kstat *stat, struct statx __user *buffer) > > ... > > + struct statx tmp; > > This function needs to be "noinline" as tmp is big. > > > - return statx_set_result(, buffer); > > + > > + return cp_statx(, buffer); > > Can you leave it as statx_set_result rather than renaming it to cp_statx? > > David I agree with using 'noinline'. But I think the name "cp_statx()" is better because it's consistent with the existing functions in the file: cp_old_stat() cp_new_stat() cp_new_stat64() - Eric
Re: [PATCH v3] statx: optimize copy of struct statx to userspace
Hi David, On Sun, Mar 12, 2017 at 09:11:53AM +, David Howells wrote: > Eric Biggers wrote: > > > +static int cp_statx(const struct kstat *stat, struct statx __user *buffer) > > ... > > + struct statx tmp; > > This function needs to be "noinline" as tmp is big. > > > - return statx_set_result(, buffer); > > + > > + return cp_statx(, buffer); > > Can you leave it as statx_set_result rather than renaming it to cp_statx? > > David I agree with using 'noinline'. But I think the name "cp_statx()" is better because it's consistent with the existing functions in the file: cp_old_stat() cp_new_stat() cp_new_stat64() - Eric
Re: [PATCH v3] statx: optimize copy of struct statx to userspace
Eric Biggerswrote: > +static int cp_statx(const struct kstat *stat, struct statx __user *buffer) > ... > + struct statx tmp; This function needs to be "noinline" as tmp is big. > - return statx_set_result(, buffer); > + > + return cp_statx(, buffer); Can you leave it as statx_set_result rather than renaming it to cp_statx? David
Re: [PATCH v3] statx: optimize copy of struct statx to userspace
Eric Biggers wrote: > +static int cp_statx(const struct kstat *stat, struct statx __user *buffer) > ... > + struct statx tmp; This function needs to be "noinline" as tmp is big. > - return statx_set_result(, buffer); > + > + return cp_statx(, buffer); Can you leave it as statx_set_result rather than renaming it to cp_statx? David
[PATCH v3] statx: optimize copy of struct statx to userspace
From: Eric BiggersI found that statx() was significantly slower than stat(). As a microbenchmark, I compared 10,000,000 invocations of fstat() on a tmpfs file to the same with statx() passed a NULL path: $ time ./stat_benchmark real0m1.464s user0m0.275s sys 0m1.187s $ time ./statx_benchmark real0m5.530s user0m0.281s sys 0m5.247s statx is expected to be a little slower than stat because struct statx is larger than struct stat, but not by *that* much. It turns out that most of the overhead was in copying struct statx to userspace, mostly in all the stac/clac instructions that got generated for each __put_user() call. (This was on x86_64, but some other architectures, e.g. arm64, have something similar now too.) stat() instead initializes its struct on the stack and copies it to userspace with a single call to copy_to_user(). This turns out to be much faster, and changing statx to do this makes it almost as fast as stat: $ time ./statx_benchmark real0m1.624s user0m0.270s sys 0m1.354s Implementation-wise, for zeroing the reserved fields, I chose to simply start by zeroing the full struct with memset. This makes it clear that every byte copied to userspace is initialized, even implicit padding bytes (though there are none currently). In the scenarios I tested, it also performed the same as a designated initializer. Manually initializing each field was still slightly faster, but would have been more error-prone and less verifiable. Signed-off-by: Eric Biggers --- fs/stat.c | 73 +++ 1 file changed, 31 insertions(+), 42 deletions(-) diff --git a/fs/stat.c b/fs/stat.c index fa0be59340cc..3fbecbfa6975 100644 --- a/fs/stat.c +++ b/fs/stat.c @@ -509,46 +509,36 @@ SYSCALL_DEFINE4(fstatat64, int, dfd, const char __user *, filename, } #endif /* __ARCH_WANT_STAT64 || __ARCH_WANT_COMPAT_STAT64 */ -static inline int __put_timestamp(struct timespec *kts, - struct statx_timestamp __user *uts) +static int cp_statx(const struct kstat *stat, struct statx __user *buffer) { - return (__put_user(kts->tv_sec, >tv_sec) || - __put_user(kts->tv_nsec,>tv_nsec ) || - __put_user(0, >__reserved)); -} - -/* - * Set the statx results. - */ -static long statx_set_result(struct kstat *stat, struct statx __user *buffer) -{ - uid_t uid = from_kuid_munged(current_user_ns(), stat->uid); - gid_t gid = from_kgid_munged(current_user_ns(), stat->gid); - - if (__put_user(stat->result_mask, >stx_mask ) || - __put_user(stat->mode, >stx_mode ) || - __clear_user(>__spare0, sizeof(buffer->__spare0)) || - __put_user(stat->nlink, >stx_nlink ) || - __put_user(uid, >stx_uid) || - __put_user(gid, >stx_gid) || - __put_user(stat->attributes,>stx_attributes ) || - __put_user(stat->blksize, >stx_blksize) || - __put_user(MAJOR(stat->rdev), >stx_rdev_major ) || - __put_user(MINOR(stat->rdev), >stx_rdev_minor ) || - __put_user(MAJOR(stat->dev),>stx_dev_major ) || - __put_user(MINOR(stat->dev),>stx_dev_minor ) || - __put_timestamp(>atime, >stx_atime ) || - __put_timestamp(>btime, >stx_btime ) || - __put_timestamp(>ctime, >stx_ctime ) || - __put_timestamp(>mtime, >stx_mtime ) || - __put_user(stat->ino, >stx_ino) || - __put_user(stat->size, >stx_size ) || - __put_user(stat->blocks,>stx_blocks ) || - __clear_user(>__spare1, sizeof(buffer->__spare1)) || - __clear_user(>__spare2, sizeof(buffer->__spare2))) - return -EFAULT; - - return 0; + struct statx tmp; + + memset(, 0, sizeof(tmp)); + + tmp.stx_mask = stat->result_mask; + tmp.stx_blksize = stat->blksize; + tmp.stx_attributes = stat->attributes; + tmp.stx_nlink = stat->nlink; + tmp.stx_uid = from_kuid_munged(current_user_ns(), stat->uid); + tmp.stx_gid = from_kgid_munged(current_user_ns(), stat->gid); + tmp.stx_mode = stat->mode; + tmp.stx_ino = stat->ino; + tmp.stx_size = stat->size; + tmp.stx_blocks = stat->blocks; + tmp.stx_atime.tv_sec = stat->atime.tv_sec; + tmp.stx_atime.tv_nsec = stat->atime.tv_nsec; + tmp.stx_btime.tv_sec = stat->btime.tv_sec; + tmp.stx_btime.tv_nsec = stat->btime.tv_nsec; + tmp.stx_ctime.tv_sec = stat->ctime.tv_sec;
[PATCH v3] statx: optimize copy of struct statx to userspace
From: Eric Biggers I found that statx() was significantly slower than stat(). As a microbenchmark, I compared 10,000,000 invocations of fstat() on a tmpfs file to the same with statx() passed a NULL path: $ time ./stat_benchmark real0m1.464s user0m0.275s sys 0m1.187s $ time ./statx_benchmark real0m5.530s user0m0.281s sys 0m5.247s statx is expected to be a little slower than stat because struct statx is larger than struct stat, but not by *that* much. It turns out that most of the overhead was in copying struct statx to userspace, mostly in all the stac/clac instructions that got generated for each __put_user() call. (This was on x86_64, but some other architectures, e.g. arm64, have something similar now too.) stat() instead initializes its struct on the stack and copies it to userspace with a single call to copy_to_user(). This turns out to be much faster, and changing statx to do this makes it almost as fast as stat: $ time ./statx_benchmark real0m1.624s user0m0.270s sys 0m1.354s Implementation-wise, for zeroing the reserved fields, I chose to simply start by zeroing the full struct with memset. This makes it clear that every byte copied to userspace is initialized, even implicit padding bytes (though there are none currently). In the scenarios I tested, it also performed the same as a designated initializer. Manually initializing each field was still slightly faster, but would have been more error-prone and less verifiable. Signed-off-by: Eric Biggers --- fs/stat.c | 73 +++ 1 file changed, 31 insertions(+), 42 deletions(-) diff --git a/fs/stat.c b/fs/stat.c index fa0be59340cc..3fbecbfa6975 100644 --- a/fs/stat.c +++ b/fs/stat.c @@ -509,46 +509,36 @@ SYSCALL_DEFINE4(fstatat64, int, dfd, const char __user *, filename, } #endif /* __ARCH_WANT_STAT64 || __ARCH_WANT_COMPAT_STAT64 */ -static inline int __put_timestamp(struct timespec *kts, - struct statx_timestamp __user *uts) +static int cp_statx(const struct kstat *stat, struct statx __user *buffer) { - return (__put_user(kts->tv_sec, >tv_sec) || - __put_user(kts->tv_nsec,>tv_nsec ) || - __put_user(0, >__reserved)); -} - -/* - * Set the statx results. - */ -static long statx_set_result(struct kstat *stat, struct statx __user *buffer) -{ - uid_t uid = from_kuid_munged(current_user_ns(), stat->uid); - gid_t gid = from_kgid_munged(current_user_ns(), stat->gid); - - if (__put_user(stat->result_mask, >stx_mask ) || - __put_user(stat->mode, >stx_mode ) || - __clear_user(>__spare0, sizeof(buffer->__spare0)) || - __put_user(stat->nlink, >stx_nlink ) || - __put_user(uid, >stx_uid) || - __put_user(gid, >stx_gid) || - __put_user(stat->attributes,>stx_attributes ) || - __put_user(stat->blksize, >stx_blksize) || - __put_user(MAJOR(stat->rdev), >stx_rdev_major ) || - __put_user(MINOR(stat->rdev), >stx_rdev_minor ) || - __put_user(MAJOR(stat->dev),>stx_dev_major ) || - __put_user(MINOR(stat->dev),>stx_dev_minor ) || - __put_timestamp(>atime, >stx_atime ) || - __put_timestamp(>btime, >stx_btime ) || - __put_timestamp(>ctime, >stx_ctime ) || - __put_timestamp(>mtime, >stx_mtime ) || - __put_user(stat->ino, >stx_ino) || - __put_user(stat->size, >stx_size ) || - __put_user(stat->blocks,>stx_blocks ) || - __clear_user(>__spare1, sizeof(buffer->__spare1)) || - __clear_user(>__spare2, sizeof(buffer->__spare2))) - return -EFAULT; - - return 0; + struct statx tmp; + + memset(, 0, sizeof(tmp)); + + tmp.stx_mask = stat->result_mask; + tmp.stx_blksize = stat->blksize; + tmp.stx_attributes = stat->attributes; + tmp.stx_nlink = stat->nlink; + tmp.stx_uid = from_kuid_munged(current_user_ns(), stat->uid); + tmp.stx_gid = from_kgid_munged(current_user_ns(), stat->gid); + tmp.stx_mode = stat->mode; + tmp.stx_ino = stat->ino; + tmp.stx_size = stat->size; + tmp.stx_blocks = stat->blocks; + tmp.stx_atime.tv_sec = stat->atime.tv_sec; + tmp.stx_atime.tv_nsec = stat->atime.tv_nsec; + tmp.stx_btime.tv_sec = stat->btime.tv_sec; + tmp.stx_btime.tv_nsec = stat->btime.tv_nsec; + tmp.stx_ctime.tv_sec = stat->ctime.tv_sec; + tmp.stx_ctime.tv_nsec =