Messages in this thread |  | | From | John Ogness <> | Subject | [RFC PATCH v3 0/2] printk: new ringbuffer implementation | Date | Sat, 27 Jul 2019 03:33:31 +0200 |
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Hello,
This is a follow-up RFC on the work to re-implement much of the core of printk. The threads for the previous RFC versions are here: v1[0], v2[1].
As was planned[2], this is only the first piece: a new lockless ringbuffer.
Changes from v2:
- Moved all code into kernel/printk/. Let's keep it private for now.
- Split the ringbuffer into 3 components:
* a data ringbuffer (dataring) to manage the raw data and data descriptors
* a numbered list (numlist) to manage committed entries and their sequence numbers
* the printk_ringbuffer, which is the high-level structure providing the reader/writer API and glue for the other structures
Splitting the components apart helped to document their roles and their related memory barriers (and will hopefully also simplify the review process).
- Renamed most functions, structures, and variables based on v2 feedback.
- Rewrote and reformatted nearly all comments (particularly the memory barrier comments) based on v2 feedback.
- Addressed implementation issues with v2:
* invalid data blocks potentially becoming valid because of overflows
* weak associations between data blocks and descriptors
* excessive freeing of data blocks due to unavailable descriptors
- Improved error handling and data integrity checks in the test module.
For the memory barrier work I wrote a litmus test for nearly every memory barrier. I did not include these in the series. Should I? If yes, where should they be placed?
I would like to point out that Petr Mladek posted a proof-of-concept[3] alternate implementation. I wanted to base my v3 on his work, but ran into too many problems getting it to run acceptably. I will address those issues in that thread. This is why my v3 is based directly on my v2.
John Ogness
[0] https://lkml.kernel.org/r/20190212143003.48446-1-john.ogness@linutronix.de [1] https://lkml.kernel.org/r/20190607162349.18199-1-john.ogness@linutronix.de [2] https://lkml.kernel.org/r/87y35hn6ih.fsf@linutronix.de [3] https://lkml.kernel.org/r/20190704103321.10022-1-pmladek@suse.com
John Ogness (2): printk-rb: add a new printk ringbuffer implementation printk-rb: add test module
kernel/printk/Makefile | 5 + kernel/printk/dataring.c | 761 ++++++++++++++++++++++++++++++++++++++++++ kernel/printk/dataring.h | 95 ++++++ kernel/printk/numlist.c | 375 +++++++++++++++++++++ kernel/printk/numlist.h | 72 ++++ kernel/printk/ringbuffer.c | 800 +++++++++++++++++++++++++++++++++++++++++++++ kernel/printk/ringbuffer.h | 288 ++++++++++++++++ kernel/printk/test_prb.c | 256 +++++++++++++++ 8 files changed, 2652 insertions(+) create mode 100644 kernel/printk/dataring.c create mode 100644 kernel/printk/dataring.h create mode 100644 kernel/printk/numlist.c create mode 100644 kernel/printk/numlist.h create mode 100644 kernel/printk/ringbuffer.c create mode 100644 kernel/printk/ringbuffer.h create mode 100644 kernel/printk/test_prb.c
-- 2.11.0
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