On compositors that forces us to double buffer, we need to re-apply
the last frame’s damage to the current frame (which uses the buffer
from the next-to-last frame).
General cell updates are handled by simply copying from the last
frame’s pixman buffer to the current frame’s.
In an attempt to improve performance, scroll damage were up until now
handled by re-playing the last frame’s scroll damage (on the current
frame’s buffer). This does not work, and resulted in glitches when
scrolling in the scrollback.
This patch does the following:
* grid_render_scroll{,_reverse}() now update the buffer’s "dirty"
region. This means the generic copy-old-frames-buffer handles the
scroll damage (albeit in, potentially, a less efficient way).
* Tracking of, and re-applying old scroll damage is completely
removed.
Closes#1173
This allows a caller to return a buffer (obtained with
shm_get_buffer()) to the pool,
The buffer must not have been used. I.e. it must not have been
attached and committed to a wayland surface.
POSIX.1-2008 has marked gettimeofday(2) as obsolete, recommending the
use of clock_gettime(2) instead.
CLOCK_MONOTONIC has been used instead of CLOCK_REALTIME because it is
unaffected by manual changes in the system clock. This makes it better
for our purposes, namely, measuring the difference between two points in
time.
tv_sec has been casted to long in most places since POSIX does not
define the actual type of time_t.
When going through the cached buffers, we only set buffer->busy on
the *first* re-usable buffer we found.
In some cases, we will find more than one re-usable buffer. In this
case, we select the “youngest” one (i.e the one most recently used, in
the hopes that we can use damage tracking instead of re-rendering the
entire buffer).
If the “current” buffer is younger than the previously detected,
re-usable, buffer, then we unref:ed the previously selected buffer,
and replaced it with the current one.
But, we did not sanitize it. That is, we did not:
* set buffer->busy
* clear its dirty region
* clear its scroll damage
That buffer would eventually get rendered to, and committed to the
compositor. Later, the compositor would free it. And there, in our
buffer_release() callback, we’d assert that buffer->busy was
set. And fail.
Closes#844
When a zero-sized buffer is requested, simply return a NULL buffer,
instead of crashing with a Wayland protocol error.
This makes it easier to request many buffers, where some may be
zero-sized, without having to pack the width/height and bufs arrays.
There may be buffers left, if their destruction has been
deferred. However, they should be on the 'deferred' list, not the
chain's buffer list.
If there are buffers left on the chain's list, that means someone
forgot to call shm_unref().
There's no longer any need to defer purging of mismatching buffer
(i.e. buffers whose width/height doesn't match the requested ones) to
after the cache lookup loop.
Up until now, *all* buffers have been tracked in a single, global
buffer list. We've used 'cookies' to separate buffers from different
contexts (so that shm_get_buffer() doesn't try to re-use e.g. a
search-box buffer for the main grid).
This patch refactors this, and completely removes the global
list.
Instead of cookies, we now use 'chains'. A chain tracks both the
properties to apply to newly created buffers (scrollable, number of
pixman instances to instantiate etc), as well as the instantiated
buffers themselves.
This means there's strictly speaking not much use for shm_fini()
anymore, since its up to the chain owner to call shm_chain_free(),
which will also purge all buffers.
However, since purging a buffer may be deferred, if the buffer is
owned by the compositor at the time of the call to shm_purge() or
shm_chain_free(), we still keep a global 'deferred' list, on to which
deferred buffers are pushed. shm_fini() iterates this list and
destroys the buffers _even_ if they are still owned by the
compositor. This only happens at program termination, and not when
destroying a terminal instance. I.e. closing a window in a “foot
--server” does *not* trigger this.
Each terminal instatiates a number of chains, and these chains are
destroyed when the terminal instance is destroyed. Note that some
buffers may be put on the deferred list, as mentioned above.
When unref:ing a "busy" buffer, destruction is (still) deferred to the
buffer release event.
However, we now move the buffer off the buffer list immediately, and
instead push it to a 'deferred' list. This prevents buffer re-use of
buffers scheduled for destruction.
It also means less buffers to iterate through when trying to find a
re-usable buffer in shm_get_buffer(), since we no longer have to wade
through a potentially long list of to-be-deleted buffers.
The initial ref-count is either 1 or 0, depending on whether the
buffer is supposed to be released "immeidately" (meaning, as soon as
the compositor releases it).
Two new user facing functions have been added: shm_addref() and
shm_unref().
Our renderer now uses these two functions instead of manually setting
and clearing the 'locked' attribute.
shm_unref() will decrement the ref-counter, and destroy the buffer
when the counter reaches zero. Except if the buffer is currently
"busy" (compositor owned), in which case destruction is deferred to
the release event. The buffer is still removed from the list though.
It may happen that we end up with multiple non-busy, same-sized
buffers for the same cookie (context), and thus eligible for re-use.
Before this patch, we would keep all those buffers around. This is
completely unnecessary. Under normal circumstances, we’ll either be
re-using a single buffer, or swap between two. In the second case, the
“other” buffer is always busy, and thus not eligible for re-use.
So, if we _do_ detect multiple, re-usable buffers, pick the one with
the lowest “age” (increasing the chance of applying damage tracking,
instead of re-drawing everything), and mark the other one for purging.
shm_get_many() always returns new buffers (i.e. never old, cached
ones). The newly allocated buffers are also marked for immediate
purging, meaning they’ll be destroyed on the next call to either
shm_get_buffer(), or shm_get_many().
Furthermore, we add a new attribute, ‘locked’, to the buffer
struct. When auto purging buffers, look at this instead of comparing
cookies.
Buffer consumers are expected to set ‘locked’ while they hold a
reference to it, and don’t want it destroyed behind their back.
This fixes an issue where we ended up "double closing" buffer FDs.
In many cases (especially on compositors with SSDs) this was pretty
rare. And even when it did happen, the FD was normally unused, and
thus nothing bad happened.
However, by quickly resizing the window while using CSDs, it was
fairly easy to trigger this. We sometimes ended up closing the
TIOCSWINCH timer FD while thinking it was a buffer FD, but most of the
times we just ended up closing _another_ buffer’s pool FD, leading to
an immediate disconnect by the compositor.
The only reason to keep the pool FD open is if we’re going to SHM
scroll the buffer; we need the FD for fallocate(FALLOC_FL_PUNCH_HOLE).
In all other cases, there’s absolutely no need to keep the FD
open. Thus, close it as soon as we’ve instantiated the buffer. This
frees up FDs, and help keep foot from FD ulimit.
* Break out cursor cell dirtying to separate functions
* Break out handling of double buffering
* Handle buffers with age > 1 (we’re swapping between more than 2
buffers)
* Detect full screen repaints, and skip re-applying old frame’s damage
* Use an allocated array insted of a tll list for old frame’s scroll damage
* When logging frame rendering time, including the amount used for
double buffering.
By default, age all matching buffers that are busy (i.e. in use by the
compositor).
This allows us to detect whether we can apply the current frame’s
damage directly, or if we need to prepare the buffer first (e.g. copy
old buffer, or re-apply last frame’s damage etc).
shm.c:301:26: error: implicit declaration of function 'fallocate' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
can_punch_hole = fallocate(
^
shm.c:302:22: error: use of undeclared identifier 'FALLOC_FL_PUNCH_HOLE'
pool_fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, 0, 1) == 0;
^
shm.c:302:45: error: use of undeclared identifier 'FALLOC_FL_KEEP_SIZE'
pool_fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, 0, 1) == 0;
^
shm.c:432:9: error: implicit declaration of function 'fallocate' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
if (fallocate(
^
shm.c:434:13: error: use of undeclared identifier 'FALLOC_FL_PUNCH_HOLE'
FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
^
shm.c:434:36: error: use of undeclared identifier 'FALLOC_FL_KEEP_SIZE'
FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
^
shm.c:501:9: error: implicit declaration of function 'fallocate' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
if (fallocate(
^
shm.c:503:13: error: use of undeclared identifier 'FALLOC_FL_PUNCH_HOLE'
FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
^
shm.c:503:36: error: use of undeclared identifier 'FALLOC_FL_KEEP_SIZE'
FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
^
shm.c:597:9: error: implicit declaration of function 'fallocate' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
if (fallocate(
^
shm.c:599:13: error: use of undeclared identifier 'FALLOC_FL_PUNCH_HOLE'
FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
^
shm.c:599:36: error: use of undeclared identifier 'FALLOC_FL_KEEP_SIZE'
FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
^
Our home rolled clip-to-cell code was, obviously, not correct.
The original problem was that we couldn't use pixman clipping since we
have multiple threads writing to the same pixman image, and thus there
would be races between the threads setting clipping.
The fix is actually simple - just instantiate one pixman
image (referencing the same backing image data) for each rendering
thread.
This both prevents accidental resizing of the memfd, and allows the
Wayland server to optimze reads from the buffer - it no longer has to
setup SIGBUS handlers.
This lessens the burden on (primarily) the compositor, since we no
longer tear down and re-create the SHM pool when scrolling.
The SHM pool is setup once, and its size is fixed at the maximum
allowed (512MB for now, 2GB would be possible).
This also allows us to mmap() the memfd once. The exposed raw pointer
is simply an offset from the memfd mmapping.
Note that this means e.g. rouge rendering code will be able to write
outside the buffer.
Finally, only do this if the caller explicitly wants to enable
scrolling. The memfd of other buffers are sized to the requested size.
* Impose a maximum memfd size limit. In theory, this can be
2GB (wl_shm_create_pool() is the limiting factor - its size argument
is an int32_t). For now, use 256MB.
This is mainly to reduce the amount of virtual address space used by
the compositor, which keeps at least one mmapping (of the entire
memfd) around. One mmapping *per terminal window* that is.
Given that we have 128TB with 48-bit virtual addresses, we could
probably bump this to 2GB without any issues. However, 256MB should
be enough.
TODO: check how much we typically move the offset when scrolling in
a fullscreen window on a 4K monitor. 256MB may turn out to be too
small.
On 32-bit shm_scroll() is completely disabled. There simply isn't
enough address space.
* Wrapping is done by moving the offset to "the other end" of the
memfd, and copying the buffer contents to the new, wrapped offset.
The "normal" scrolling code then does the actual scrolling. This
means we'll re-instantiate all objects twice when wrapping.
Implemented by truncating the file size and moving the offset
backwards. This means we can only reverse scroll when we've previously
scrolled forward.
TODO: figure out if we can somehow do fast reverse scrolling even
though offset is 0 (or well, less than required for scrolling).
