This RFC is collecting more feedbacks to device when is good time to remove whole async_tx framework and how to remove it safely. And is overall direction correction.
Little to no real hardware acceleration usage: Most systems run RAID5/6 parity calculations on the CPU using optimized XOR/PQ implementations, while DMAEngine-backed async_tx acceleration is rarely present or exercised. Added abstraction and maintenance cost: async_tx introduces an extra layer between MD RAID and parity operations, making the code harder to understand, debug, and maintain. Modern CPUs outperform DMA offload: SIMD implementations (SSE/AVX/NEON and architecture-specific RAID routines) often provide better performance than DMA descriptor setup and completion handling overhead. Obsolete hardware dependencies: Many async_tx acceleration backends were designed for older DMA/XOR engines that are no longer common in contemporary systems. Complex asynchronous execution model: Dependency chains, callback handling, and DMA transaction management increase code complexity without corresponding performance benefits on typical deployments.Simplifies RAID code paths: Removing async_tx allows direct use of synchronous XOR/PQ helpers, reducing indirection in raid5.c source code [linux/drivers/md/raid5.c]. Reduces testing burden: Eliminates rarely used code paths that are difficult to validate and more likely to accumulate latent bugs. Aligns implementation with actual usage: The vast majority of MD RAID deployments already rely on software parity generation rather than DMA offload. Current dmaengine support xor is Driver File Driver Name First Added Date ========================================================================== mv_xor.c Marvell XOR Engine (mv_xor) 2008-07-08 ppc4xx/adma.c ppc440spe ADMA (PPC4xx) 2009-12-11 fsl_raid.c Freescale RAID Engine (fsl_re) 2015-03-03 xgene-dma.c APM X-Gene DMA 2015-03-18 ioat/init.c Intel IOAT DMA (ioatdma) 2015-08-11 mv_xor_v2.c Marvell XOR Engine v2 2016-06-16 bcm-sba-raid.c BCM SBA RAID (Broadcom) 2017-05-15 fsl_raid is for power pc SoC, which already EOF. Patches is build test only now. To: Alasdair Kergon <[email protected]> To: Mike Snitzer <[email protected]> To: Mikulas Patocka <[email protected]> To: Benjamin Marzinski <[email protected]> To: Song Liu <[email protected]> To: Yu Kuai <[email protected]> To: Li Nan <[email protected]> To: Xiao Ni <[email protected]> To: Dan Williams <[email protected]> To: Herbert Xu <[email protected]> To: "David S. Miller" <[email protected]> To: Jonathan Corbet <[email protected]> To: Shuah Khan <[email protected]> To: Randy Dunlap <[email protected]> Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: [email protected] Cc: Anatolij Gustschin <[email protected]> Cc: Saeed Bishara <[email protected]> Cc: Rameshwar Prasad Sahu <[email protected]> Cc: Thomas Petazzoni <[email protected]> Cc: Anup Patel <[email protected]> Signed-off-by: Frank Li <[email protected]> --- Frank Li (4): md/dm-integrity: replace async_tx with synchronous xor for journal md/raid5-ppl: replace async_tx with synchronous xor md/raid5: replace async_tx with synchronous xor/pq operations crypto: remove async_tx framework Documentation/crypto/async-tx-api.rst | 270 --------------- Documentation/crypto/index.rst | 1 - crypto/Kconfig | 5 - crypto/Makefile | 4 - crypto/async_tx/Kconfig | 28 -- crypto/async_tx/Makefile | 7 - crypto/async_tx/async_memcpy.c | 97 ------ crypto/async_tx/async_pq.c | 464 -------------------------- crypto/async_tx/async_raid6_recov.c | 595 ---------------------------------- crypto/async_tx/async_tx.c | 299 ----------------- crypto/async_tx/async_xor.c | 380 ---------------------- crypto/async_tx/raid6test.c | 250 -------------- drivers/md/dm-integrity.c | 26 +- drivers/md/raid5-log.h | 4 +- drivers/md/raid5-ppl.c | 40 +-- drivers/md/raid5.c | 467 +++++++++++++------------- include/linux/async_tx.h | 187 ----------- 17 files changed, 281 insertions(+), 2843 deletions(-) --- base-commit: 98a4f6276df67a1bb37b1be56a3ab4285155e3df change-id: 20261015-asycn_tx_remove-381cd003d9f7 Best regards, -- Frank Li <[email protected]>
