Linux mainline fork with MSM8998 patches | https://mainline.space | Currently supported devices:
OnePlus 5/5T, Xiaomi Mi 6, F(x)tec Pro¹ (2019 QX1000 model) & Sony Xperia XZ Premium (UNTESTED!)
874fc35cdd
Turns out, the default setting of attr.aux_watermark to half of the total buffer size is not very useful, especially with smaller buffers. The problem is that, after half of the buffer is filled up, the kernel updates ->aux_head and sets up the next "transaction", while observing that ->aux_tail is still zero (as userspace haven't had the chance to update it), meaning that the trace will have to stop at the end of this second "transaction". This means, for example, that the second PERF_RECORD_AUX in every trace comes with TRUNCATED flag set. Setting attr.aux_watermark to quarter of the buffer gives enough space for the ->aux_tail update to be observed and prevents the data loss. The obligatory before/after showcase: > # perf_before record -e intel_pt//u -m,8 uname > Linux > [ perf record: Woken up 6 times to write data ] > Warning: > AUX data lost 4 times out of 10! > > [ perf record: Captured and wrote 0.099 MB perf.data ] > # perf record -e intel_pt//u -m,8 uname > Linux > [ perf record: Woken up 4 times to write data ] > [ perf record: Captured and wrote 0.039 MB perf.data ] The effect is still visible with large workloads and large buffers, although less pronounced. Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20210414154955.49603-3-alexander.shishkin@linux.intel.com |
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.