On 28/06/2018 11:10, Chris Wilson wrote:
Quoting Tvrtko Ursulin (2018-06-28 11:02:17)
On 27/06/2018 22:07, Chris Wilson wrote:
Following the removal of the last workarounds, the only CSB mmio access
is for the old vGPU interface. The mmio registers presented by vGPU do
not require forcewake and can be treated as ordinary volatile memory,
i.e. they behave just like the HWSP access just at a different location.
We can reduce the CSB access to a set of read/write/buffer pointers and
treat the various paths identically and not worry about forcewake.
(Forcewake is nightmare for worstcase latency, and we want to process
this all with irqsoff -- no latency allowed!)
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/i915/intel_engine_cs.c | 12 ---
drivers/gpu/drm/i915/intel_lrc.c | 116 ++++++++++--------------
drivers/gpu/drm/i915/intel_ringbuffer.h | 23 +++--
3 files changed, 65 insertions(+), 86 deletions(-)
diff --git a/drivers/gpu/drm/i915/intel_engine_cs.c b/drivers/gpu/drm/i915/intel_engine_cs.c
index d3264bd6e9dc..7209c22798e6 100644
--- a/drivers/gpu/drm/i915/intel_engine_cs.c
+++ b/drivers/gpu/drm/i915/intel_engine_cs.c
@@ -25,7 +25,6 @@
#include <drm/drm_print.h>
#include "i915_drv.h"
-#include "i915_vgpu.h"
#include "intel_ringbuffer.h"
#include "intel_lrc.h"
@@ -456,21 +455,10 @@ static void intel_engine_init_batch_pool(struct intel_engine_cs *engine)
i915_gem_batch_pool_init(&engine->batch_pool, engine);
}
-static bool csb_force_mmio(struct drm_i915_private *i915)
-{
- /* Older GVT emulation depends upon intercepting CSB mmio */
- if (intel_vgpu_active(i915) && !intel_vgpu_has_hwsp_emulation(i915))
- return true;
-
- return false;
-}
-
static void intel_engine_init_execlist(struct intel_engine_cs *engine)
{
struct intel_engine_execlists * const execlists = &engine->execlists;
- execlists->csb_use_mmio = csb_force_mmio(engine->i915);
-
execlists->port_mask = 1;
BUILD_BUG_ON_NOT_POWER_OF_2(execlists_num_ports(execlists));
GEM_BUG_ON(execlists_num_ports(execlists) > EXECLIST_MAX_PORTS);
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 91656eb2f2db..368a8c74d11d 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -137,6 +137,7 @@
#include <drm/i915_drm.h>
#include "i915_drv.h"
#include "i915_gem_render_state.h"
+#include "i915_vgpu.h"
#include "intel_lrc_reg.h"
#include "intel_mocs.h"
#include "intel_workarounds.h"
@@ -953,44 +954,23 @@ static void process_csb(struct intel_engine_cs *engine)
{
struct intel_engine_execlists * const execlists = &engine->execlists;
struct execlist_port *port = execlists->port;
- struct drm_i915_private *i915 = engine->i915;
-
- /* The HWSP contains a (cacheable) mirror of the CSB */
- const u32 *buf =
- &engine->status_page.page_addr[I915_HWS_CSB_BUF0_INDEX];
- unsigned int head, tail;
- bool fw = false;
+ const u32 * const buf = execlists->csb_status;
+ u8 head, tail;
/* Clear before reading to catch new interrupts */
clear_bit(ENGINE_IRQ_EXECLIST, &engine->irq_posted);
smp_mb__after_atomic();
- if (unlikely(execlists->csb_use_mmio)) {
- intel_uncore_forcewake_get(i915, execlists->fw_domains);
- fw = true;
-
- buf = (u32 * __force)
- (i915->regs + i915_mmio_reg_offset(RING_CONTEXT_STATUS_BUF_LO(engine, 0)));
+ /* Note that csb_write, csb_status may be either in HWSP or mmio */
+ head = execlists->csb_head;
+ tail = READ_ONCE(*execlists->csb_write);
Under GVT when this is emulated mmio I think you need to mask and shift
it with GEN8_CSB_WRITE_PTR.
Shift is 0, mask is applied by u8.
Evil. :) Put a comment please.
+ GEM_TRACE("%s cs-irq head=%d, tail=%d\n", engine->name, head, tail);
+ if (unlikely(head == tail))
+ return;
- head = readl(i915->regs + i915_mmio_reg_offset(RING_CONTEXT_STATUS_PTR(engine)));
- tail = GEN8_CSB_WRITE_PTR(head);
- head = GEN8_CSB_READ_PTR(head);
- execlists->csb_head = head;
- } else {
- const int write_idx =
- intel_hws_csb_write_index(i915) -
- I915_HWS_CSB_BUF0_INDEX;
+ rmb(); /* Hopefully paired with a wmb() in HW */
- head = execlists->csb_head;
- tail = READ_ONCE(buf[write_idx]);
- rmb(); /* Hopefully paired with a wmb() in HW */
- }
- GEM_TRACE("%s cs-irq head=%d [%d%s], tail=%d [%d%s]\n",
- engine->name,
- head, GEN8_CSB_READ_PTR(readl(i915->regs + i915_mmio_reg_offset(RING_CONTEXT_STATUS_PTR(engine)))), fw ? "" : "?",
- tail, GEN8_CSB_WRITE_PTR(readl(i915->regs + i915_mmio_reg_offset(RING_CONTEXT_STATUS_PTR(engine)))), fw ? "" : "?");
-
- while (head != tail) {
+ do {
Why convert while to do-while? Early unlikely return above handles the
void process_csb calls? Would the same effect happen if you put unlikely
in the while (head != tail) condition and would be simpler?
The earlier return to circumvent the lfence.
Oh that one.. so why it is safe to compare head and tail before the rmb
since we need the rmb afterwards?
struct i915_request *rq;
unsigned int status;
unsigned int count;
@@ -1016,12 +996,12 @@ static void process_csb(struct intel_engine_cs *engine)
* status notifier.
*/
- status = READ_ONCE(buf[2 * head]); /* maybe mmio! */
GEM_TRACE("%s csb[%d]: status=0x%08x:0x%08x, active=0x%x\n",
engine->name, head,
- status, buf[2*head + 1],
+ buf[2 * head + 0], buf[2 * head + 1],
execlists->active);
+ status = buf[2 * head];
Why not leave before GEM_TRACE above, as is, and then diff is smaller?
You made me correct the GEM_TRACE!
Hm?
Looking at it I still prefer 2 buf[] vs the mixed local/buf[].
Not touching lines which don't need touching trumps in my book. But OK.
Regards,
Tvrtko
if (status & (GEN8_CTX_STATUS_IDLE_ACTIVE |
GEN8_CTX_STATUS_PREEMPTED))
execlists_set_active(execlists,
@@ -1103,16 +1083,11 @@ static void process_csb(struct intel_engine_cs *engine)
} else {
port_set(port, port_pack(rq, count));
}
- }
+ } while (head != tail);
- if (head != execlists->csb_head) {
- execlists->csb_head = head;
- writel(_MASKED_FIELD(GEN8_CSB_READ_PTR_MASK, head << 8),
- i915->regs + i915_mmio_reg_offset(RING_CONTEXT_STATUS_PTR(engine)));
- }
-
- if (unlikely(fw))
- intel_uncore_forcewake_put(i915, execlists->fw_domains);
+ writel(_MASKED_FIELD(GEN8_CSB_READ_PTR_MASK, head << 8),
+ execlists->csb_read);
+ execlists->csb_head = head;
I guess early return helps to avoid this, but since it is going away in
a following patch maybe it is not worth it.
lfence!
-Chris
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