On Sun, Sep 22, 2024 at 04:39:53PM +0530, Ritesh Harjani wrote:

Luming Yu [off-list ref] writes:

quoted

From: Yu Luming <redacted>

ppc always do its own tracking for batch tlb. By trivially enabling
the ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH in ppc, ppc arch can re-use
common code in rmap and reduce overhead and do optimization it could not
have without a tlb flushing context at low architecture level.

I looked at this patch and other than the compile failure, this patch
still won't optimize anything. The idea of this config is that we want
to batch all the tlb flush operation at the end. By returning false from
should_defer_flush() (in this patch), we are saying we cannot defer
the flush and hence we do tlb flush in the same context of unmap.

not exactly, as false return implies, we currently do nothing but relying on
book3S_64's tlb batch implementation which contains a bit of defer optimization
that we need to use a real benchmark to do some performance characterization.

And I need to get my test bed ready for patch testing first. So I have to
defer the real optimization in this area.

Anyway, I took a quick look at ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
and I have a quick PoC for the same. I will soon post it.

thanks for picking up the barton for the future collaboration on the
potential common performance benefits among us for powerpc arch.

-ritesh

quoted

Signed-off-by: Luming Yu <redacted>
---
 arch/powerpc/Kconfig                |  1 +
 arch/powerpc/include/asm/tlbbatch.h | 30 +++++++++++++++++++++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 arch/powerpc/include/asm/tlbbatch.h

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index e94e7e4bfd40..e6db84dd014a 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig

@@ -175,6 +175,7 @@ config PPC
 	select ARCH_WANT_IPC_PARSE_VERSION
 	select ARCH_WANT_IRQS_OFF_ACTIVATE_MM
 	select ARCH_WANT_LD_ORPHAN_WARN
+	select ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
 	select ARCH_WANT_OPTIMIZE_DAX_VMEMMAP	if PPC_RADIX_MMU
 	select ARCH_WANTS_MODULES_DATA_IN_VMALLOC	if PPC_BOOK3S_32 || PPC_8xx
 	select ARCH_WEAK_RELEASE_ACQUIRE

diff --git a/arch/powerpc/include/asm/tlbbatch.h b/arch/powerpc/include/asm/tlbbatch.h
new file mode 100644
index 000000000000..484628460057
--- /dev/null
+++ b/arch/powerpc/include/asm/tlbbatch.h

@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ARCH_PPC_TLBBATCH_H
+#define _ARCH_PPC_TLBBATCH_H
+
+struct arch_tlbflush_unmap_batch {
+	/*
+         *
+	 */
+};
+
+static inline void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch)
+{
+}
+
+static inline void arch_tlbbatch_add_pending(struct arch_tlbflush_unmap_batch *batch,
+						struct mm_struct *mm,
+						unsigned long uarddr)
+{
+}
+
+static inline bool arch_tlbbatch_should_defer(struct mm_struct *mm)
+{
+	/*ppc always do tlb flush in batch*/
+	return false;
+}
+
+static inline void arch_flush_tlb_batched_pending(struct mm_struct *mm)
+{
+}
+#endif /* _ARCH_PPC_TLBBATCH_H */

-- 
2.42.0.windows.2