bpf: add cpu time counter kfuncs #8693
Closed
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
![kernel-patches-daemon-bpf[bot]](https://avatars.githubusercontent.com/u/70728002?s=60&v=4){kind=small}
|
Upstream branch: f3f8649 |
|
At least one diff in series https://patchwork.kernel.org/project/netdevbpf/list/?series=944865 expired. Closing PR. |
|
Upstream branch: a259804 |
kernel-patches-daemon-bpf
bot
added
new
V12
and removed
changes-requested
V11
V11-ci-pass
labels
kernel-patches-daemon-bpf
bot
force-pushed
the
series/911922=>bpf-next
branch
from
a06dc5b to
1206db5
Compare
kernel-patches-daemon-bpf
bot
force-pushed
the
bpf-next_base
branch
from
50dba77 to
ce294a5
Compare
|
Upstream branch: 79db658 |
kernel-patches-daemon-bpf
bot
force-pushed
the
series/911922=>bpf-next
branch
from
1206db5 to
1a4889f
Compare
kernel-patches-daemon-bpf
bot
force-pushed
the
bpf-next_base
branch
from
ce294a5 to
e34fe93
Compare
BPF JIT is moving towards optimizing kfuncs and it was long overdue to switch the dependency. Let's do it now to simplify other patches in the series. Signed-off-by: Vadim Fedorenko <[email protected]>
New kfunc to return ARCH-specific timecounter. The main reason to implement this kfunc is to avoid extra overhead of benchmark measurements, which are usually done by a pair of bpf_ktime_get_ns() at the beginnig and at the end of the code block under benchmark. When fully JITed this function doesn't implement conversion to the monotonic clock and saves some CPU cycles by receiving timecounter values in single-digit amount of instructions. The delta values can be translated into nanoseconds using kfunc introduced in the next patch. For x86_64 BPF JIT converts this kfunc into rdtsc ordered call. Other architectures will get JIT implementation too if supported. The fallback is to get CLOCK_MONOTONIC_RAW value in ns. JIT version of the function uses "LFENCE; RDTSC" variant because it doesn't care about cookie value returned by "RDTSCP" and it doesn't want to trash RCX value. LFENCE option provides the same ordering guarantee as RDTSCP variant. The simplest use-case is added in 5th patch, where we calculate the time spent by bpf_get_ns_current_pid_tgid() kfunc. More complex example is to use session cookie to store timecounter value at kprobe/uprobe using kprobe.session/uprobe.session, and calculate the difference at kretprobe/uretprobe. Acked-by: Eduard Zingerman <[email protected]> Acked-by: Andrii Nakryiko <[email protected]> Acked-by: Yonghong Song <[email protected]> Signed-off-by: Vadim Fedorenko <[email protected]>
The new helper should be used to convert deltas of values received by bpf_get_cpu_time_counter() into nanoseconds. It is not designed to do full conversion of time counter values to CLOCK_MONOTONIC_RAW nanoseconds and cannot guarantee monotonicity of 2 independent values, but rather to convert the difference of 2 close enough values of CPU timestamp counter into nanoseconds. This function is JITted into just several instructions and adds as low overhead as possible and perfectly suits benchmark use-cases. When the kfunc is not JITted it returns the value provided as argument because the kfunc in previous patch will return values in nanoseconds and can be optimized by verifier. Reviewed-by: Eduard Zingerman <[email protected]> Acked-by: Andrii Nakryiko <[email protected]> Signed-off-by: Vadim Fedorenko <[email protected]>
bpf_get_cpu_time_counter() is replaced with rdtsc instruction on x86_64. Add tests to check that JIT works as expected. When JIT is not supported, bpf_cpu_time_counter_to_ns() can be inlined by verifier. Acked-by: Eduard Zingerman <[email protected]> Signed-off-by: Vadim Fedorenko <[email protected]>
The selftest provides an example of how to measure the latency of bpf kfunc/helper call using time stamp counter and how to convert measured value into nanoseconds. Signed-off-by: Vadim Fedorenko <[email protected]>
|
Upstream branch: e16e64f |
kernel-patches-daemon-bpf
bot
force-pushed
the
series/911922=>bpf-next
branch
from
1a4889f to
69f7146
Compare
|
At least one diff in series https://patchwork.kernel.org/project/netdevbpf/list/?series=945657 expired. Closing PR. |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Pull request for series with
subject: bpf: add cpu time counter kfuncs
version: 11
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=944865