From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44378) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ejO45-0007G7-3R for qemu-devel@nongnu.org; Wed, 07 Feb 2018 06:39:02 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ejO40-0003OF-31 for qemu-devel@nongnu.org; Wed, 07 Feb 2018 06:39:01 -0500 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:58190 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1ejO3z-0003Ny-TN for qemu-devel@nongnu.org; Wed, 07 Feb 2018 06:38:56 -0500 Date: Wed, 7 Feb 2018 11:38:42 +0000 From: "Dr. David Alan Gilbert" Message-ID: <20180207113841.GB2665@work-vm> References: <20180207073331.14158-1-haozhong.zhang@intel.com> <20180207073331.14158-6-haozhong.zhang@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180207073331.14158-6-haozhong.zhang@intel.com> Subject: Re: [Qemu-devel] [PATCH v2 5/8] migration/ram: ensure write persistence on loading zero pages to PMEM List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Haozhong Zhang Cc: qemu-devel@nongnu.org, Eduardo Habkost , Igor Mammedov , Paolo Bonzini , mst@redhat.com, Xiao Guangrong , Juan Quintela , Stefan Hajnoczi , Dan Williams * Haozhong Zhang (haozhong.zhang@intel.com) wrote: > When loading a zero page, check whether it will be loaded to > persistent memory If yes, load it by libpmem function > pmem_memset_nodrain(). Combined with a call to pmem_drain() at the > end of RAM loading, we can guarantee all those zero pages are > persistently loaded. I'm surprised pmem is this invasive to be honest; I hadn't expected the need for special memcpy's etc everywhere. We're bound to miss some. I assume there's separate kernel work needed to make postcopy work; certainly the patches here don't seem to touch the postcopy path. > Depending on the host HW/SW configurations, pmem_drain() can be > "sfence". Therefore, we do not call pmem_drain() after each > pmem_memset_nodrain(), or use pmem_memset_persist() (equally > pmem_memset_nodrain() + pmem_drain()), in order to avoid unnecessary > overhead. > > Signed-off-by: Haozhong Zhang > --- > include/qemu/pmem.h | 9 +++++++++ > migration/ram.c | 34 +++++++++++++++++++++++++++++----- > 2 files changed, 38 insertions(+), 5 deletions(-) > > diff --git a/include/qemu/pmem.h b/include/qemu/pmem.h > index 9017596ff0..861d8ecc21 100644 > --- a/include/qemu/pmem.h > +++ b/include/qemu/pmem.h > @@ -26,6 +26,15 @@ pmem_memcpy_persist(void *pmemdest, const void *src, size_t len) > return memcpy(pmemdest, src, len); > } > > +static inline void *pmem_memset_nodrain(void *pmemdest, int c, size_t len) > +{ > + return memset(pmemdest, c, len); > +} > + > +static inline void pmem_drain(void) > +{ > +} > + > #endif /* CONFIG_LIBPMEM */ > > #endif /* !QEMU_PMEM_H */ > diff --git a/migration/ram.c b/migration/ram.c > index cb1950f3eb..5a0e503818 100644 > --- a/migration/ram.c > +++ b/migration/ram.c > @@ -49,6 +49,7 @@ > #include "qemu/rcu_queue.h" > #include "migration/colo.h" > #include "migration/block.h" > +#include "qemu/pmem.h" > > /***********************************************************/ > /* ram save/restore */ > @@ -2467,6 +2468,20 @@ static inline void *host_from_ram_block_offset(RAMBlock *block, > return block->host + offset; > } > > +static void ram_handle_compressed_common(void *host, uint8_t ch, uint64_t size, > + bool is_pmem) I don't think there's any advantage of splitting out this _common routine; lets just add the parameter to ram_handle_compressed. > +{ > + if (!ch && is_zero_range(host, size)) { > + return; > + } > + > + if (!is_pmem) { > + memset(host, ch, size); > + } else { > + pmem_memset_nodrain(host, ch, size); > + } I'm wondering if it would be easier to pass in a memsetfunc ptr and call that (defualting to memset if it's NULL). > +} > + > /** > * ram_handle_compressed: handle the zero page case > * > @@ -2479,9 +2494,7 @@ static inline void *host_from_ram_block_offset(RAMBlock *block, > */ > void ram_handle_compressed(void *host, uint8_t ch, uint64_t size) > { > - if (ch != 0 || !is_zero_range(host, size)) { > - memset(host, ch, size); > - } > + return ram_handle_compressed_common(host, ch, size, false); > } > > static void *do_data_decompress(void *opaque) > @@ -2823,6 +2836,7 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id) > bool postcopy_running = postcopy_is_running(); > /* ADVISE is earlier, it shows the source has the postcopy capability on */ > bool postcopy_advised = postcopy_is_advised(); > + bool need_pmem_drain = false; > > seq_iter++; > > @@ -2848,6 +2862,8 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id) > ram_addr_t addr, total_ram_bytes; > void *host = NULL; > uint8_t ch; > + RAMBlock *block = NULL; > + bool is_pmem = false; > > addr = qemu_get_be64(f); > flags = addr & ~TARGET_PAGE_MASK; > @@ -2864,7 +2880,7 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id) > > if (flags & (RAM_SAVE_FLAG_ZERO | RAM_SAVE_FLAG_PAGE | > RAM_SAVE_FLAG_COMPRESS_PAGE | RAM_SAVE_FLAG_XBZRLE)) { > - RAMBlock *block = ram_block_from_stream(f, flags); > + block = ram_block_from_stream(f, flags); > > host = host_from_ram_block_offset(block, addr); > if (!host) { > @@ -2874,6 +2890,9 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id) > } > ramblock_recv_bitmap_set(block, host); > trace_ram_load_loop(block->idstr, (uint64_t)addr, flags, host); > + > + is_pmem = ramblock_is_pmem(block); > + need_pmem_drain = need_pmem_drain || is_pmem; > } > > switch (flags & ~RAM_SAVE_FLAG_CONTINUE) { > @@ -2927,7 +2946,7 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id) > > case RAM_SAVE_FLAG_ZERO: > ch = qemu_get_byte(f); > - ram_handle_compressed(host, ch, TARGET_PAGE_SIZE); > + ram_handle_compressed_common(host, ch, TARGET_PAGE_SIZE, is_pmem); > break; > > case RAM_SAVE_FLAG_PAGE: > @@ -2970,6 +2989,11 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id) > } > > wait_for_decompress_done(); > + > + if (need_pmem_drain) { > + pmem_drain(); > + } > + > rcu_read_unlock(); > trace_ram_load_complete(ret, seq_iter); > return ret; > -- > 2.14.1 Dave > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK