From: Jim Cromie <jim.cromie@gmail.com>
To: jbaron@akamai.com, gregkh@linuxfoundation.org,
linux-kernel@vger.kernel.org
Cc: Jim Cromie <jim.cromie@gmail.com>
Subject: [RFC PATCH v2 16/19] dyndbg: ddebug_site_get/put api commentary
Date: Fri, 25 Dec 2020 13:19:41 -0700 [thread overview]
Message-ID: <20201225201944.3701590-17-jim.cromie@gmail.com> (raw)
In-Reply-To: <20201225201944.3701590-1-jim.cromie@gmail.com>
Paths forward: (not mutually exclusive)
A: !site -> fill from backing store
1st try at this is/was using zram. At init, it copied each callsite
into a zs-allocation, and all site-> refs afterward went thru
_get/_put to zs-map on demand, and zs-unmap the site info. This
worked until I tried to keep callsites mapped while they're enabled.
Another approach is to compress the new linker section, using some
algo thats good at indexed decompression. I tried to test this a bit,
using objcopy, unsuccessfully:
objcopy --dump-section __dyndbg_callsites=dd_callsites vmlinux.o
From vmlinux.o it was mostly empty, vmlinux didnt have the section.
B: callsite as a set of property vectors, indexed by 'N'
We know dp is in a vector, either in the builtin __dyndbg_callsite
linker section, or the same from a modprobed one. The builtin section
has all builtin module sub-sections catenated dogether.
At init, we iterate over the section, and "parse it" by creating a
ddebug_table for each module with prdebugs. ddebug_table.num_debugs
remembers the size of each modules' vector of prdebugs.
We need a few things:
- _ddebug.index field, which knows offset to start of this sub-vector.
this new field will be "free" because the struct has padding.
it can be initialized during init, then RO.
- a back-pointer at the beginning of the sub-vector, to the
ddebug_table "owning" (but not containing) this sub-vector of
prdebugs.
If we had both, we could get from the ddebug element to its vector
root, back up to the owning ddebug_table, then down to the _callsite
vector, and index to the right element. While slower than a pointer
deref, this is a cold path, and it allows elimination of the
per-callsite pointer member, thus greater density of the sections, and
still can support sparse site info.
That back-pointer feels tricky. It needs to be 1st in the sub-vector
is to reserve the 0th slot
ing its spot at the
front of
each module's ddebug sub-vector.
getting space in the
section for it. Initializing it is easy.
prdebugs are added to section when DECLARE_DYAMIC_DEBUG_METADATA is
compiled; its unclear whether they are intrinsically sorted during
compile, or whether thats a linker thing.
Ideally, a MODULE-mumble declaration can be coaxed into declaring a
module singleton in the section(s), either naturally at the top (or
bottom) or sorted into place.
If that doesn't work, a "preload if module is different" strategy
could maybe work, but I dont know how to do that in macros.
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
lib/dynamic_debug.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/lib/dynamic_debug.c b/lib/dynamic_debug.c
index 25f49515c235..ec28c113a361 100644
--- a/lib/dynamic_debug.c
+++ b/lib/dynamic_debug.c
@@ -146,7 +146,7 @@ static void vpr_info_dq(const struct ddebug_query *query, const char *msg)
static struct _ddebug_callsite *ddebug_site_get(struct _ddebug *dp)
{
- return dp->site;
+ return dp->site; /* passthru abstraction */
}
static inline void ddebug_site_put(struct _ddebug *dp)
{
--
2.29.2
next prev parent reply other threads:[~2020-12-25 20:22 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-25 20:19 [RFC PATCH v2 00/19] dynamic debug diet plan Jim Cromie
2020-12-25 20:19 ` [RFC PATCH v2 01/19] dyndbg: fix use before null check Jim Cromie
2020-12-25 20:19 ` [RFC PATCH v2 02/19] dyndbg: split struct _ddebug, move display fields to new _ddebug_callsite Jim Cromie
2020-12-31 2:34 ` [dyndbg] e83b4a5011: leaking-addresses.proc.__dyndbg_callsites kernel test robot
2020-12-25 20:19 ` [RFC PATCH v2 03/19] dyndbg: refactor part of ddebug_change to ddebug_match_site Jim Cromie
2020-12-25 20:19 ` [RFC PATCH v2 04/19] dyndbg: accept null site in ddebug_match_site Jim Cromie
2020-12-25 20:19 ` [RFC PATCH v2 05/19] dyndbg: hoist ->site out of ddebug_match_site Jim Cromie
2020-12-25 20:19 ` [RFC PATCH v2 06/19] dyndbg: accept null site in ddebug_change Jim Cromie
2020-12-25 20:19 ` [RFC PATCH v2 07/19] dyndbg: accept null site in dynamic_emit_prefix Jim Cromie
2020-12-25 20:19 ` [RFC PATCH v2 08/19] dyndbg: accept null site in ddebug_proc_show Jim Cromie
2020-12-25 20:19 ` [RFC PATCH v2 09/19] dyndbg: optimize ddebug_emit_prefix Jim Cromie
2020-12-25 20:19 ` [RFC PATCH v2 10/19] dyndbg: avoid calling dyndbg_emit_prefix when it has no work Jim Cromie
2020-12-25 20:19 ` [RFC PATCH v2 11/19] dyndbg: refactor ddebug_alter_site out of ddebug_change Jim Cromie
2020-12-25 20:19 ` [RFC PATCH v2 12/19] dyndbg: allow deleting site info via control interface Jim Cromie
2020-12-25 20:19 ` [RFC PATCH v2 13/19] dyndbg: verify __dyndbg & __dyndbg_callsite invariant Jim Cromie
2020-12-25 20:19 ` [RFC PATCH v2 14/19] dyndbg+module: expose ddebug_callsites to modules Jim Cromie
2020-12-25 20:19 ` [RFC PATCH v2 15/19] dyndbg: add ddebug_site_get/put api with pass-thru impl Jim Cromie
2020-12-25 20:19 ` Jim Cromie [this message]
2020-12-25 20:19 ` [RFC PATCH v2 17/19] dyndbg: rearrange struct ddebug_callsites Jim Cromie
2020-12-25 20:19 ` [RFC PATCH v2 18/19] dyndbg: add module_index to struct _ddebug Jim Cromie
2020-12-25 20:19 ` [RFC PATCH v2 19/19] dyndbg: try DEFINE_DYNAMIC_DEBUG_TABLE Jim Cromie
2020-12-29 18:56 ` [RFC PATCH v2 00/19] dynamic debug diet plan Joe Perches
2021-01-06 17:50 ` jim.cromie
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